[[quoteright:225:http://static.tvtropes.org/pmwiki/pub/images/ThreeInvestigators_TerrorCastle_3742.jpeg]]
[[caption-width-right:225:Creator/AlfredHitchcock: The Secret of Terror Castle.]]

''The Three Investigators'' was a juvenile detective book series written by Creator/RobertArthurJr, originally called "Creator/AlfredHitchcock and the Three Investigators". It centered on a trio of high school boys who live in the fictional town of Rocky Beach, California. They are:

'''[[TheHero Jupiter Jones]]''', '''[[TheLeader First Investigator]]'''. Head of the firm and known for his remarkable powers of observation and deduction, he is stocky, muscular, and a bit roly-poly. He has a round face which often looks stupid but which hides a sharp intelligence. Jupiter has an excellent mind, and he is rather proud of it. He has many good features, but undue modesty is not one of them.

'''[[TheBigGuy Pete Crenshaw]]''', '''[[TheLancer Second Investigator]]'''. Tall and muscular, sturdy and courageous, he excels at athletics. [[CowardlyLion Inclined to nervousness before anything happens]], but a tower of strength in any kind of trouble. He is Jupiter's right-hand man when it comes to trailing suspects and other dangerous activities. Pete's father is a special-effects man who works at one of the movie studios in Hollywood.

'''[[AudienceSurrogate Bob Andrews]]''', '''[[TheSmartGuy Records and Research]]'''. Slight of build, small but wiry. Studious in nature, he is something of a scholarly type with an adventurous spirit. He has great nerve and the courage of a lion. Adept at research, he works part-time at the local library which enables him to hunt up information needed for their investigations. Bob's father is a feature writer for a big newspaper in Los Angeles.

The boys spend their free time solving various mysteries rather than true crimes, mysteries which tended to be far more bizarre, unusual, complex, and intriguing than those of ''Literature/TheHardyBoys'' and other KidDetective books of the day, and with protagonists who were simply ordinary, middle-class American boys, without the riches or special advantages of sleuths such as, again, ''TheHardyBoys'' or ''Literature/NancyDrew'', both of which had famous fathers who helped them out in their cases a great deal.

The three boys make an excellent team. Having formed the firm of The Three Investigators, they use their spare time to solve any riddles, enigmas and mysteries that come their way. Their motto is "We Investigate Anything". Headquarters for The Three Investigators is a damaged 30-foot mobile home trailer within the salvage yard run by Jupiter's Uncle Titus and Aunt Mathilda which has been cleverly hidden from view by stacks of junk which surround it. It is accessible only by several secret passages and hidden entrances including their favorite, [[ThemeNaming Tunnel Two]]. Headquarters contains a small laboratory, a dark room, and an office with a desk, typewriter, telephone, tape recorder and reference books. All of their equipment was rebuilt from junk that came into the salvage yard.

For traveling long distances, the boys have the use of a gold-plated Rolls Royce, complete with a chauffeur, Worthington. Jupiter won the use of this auto, for thirty days, in a contest. (A grateful client from the seventh book in the series, ''The Mystery of the Fiery Eye'', [[HandWave indefinitely extended the time that they could make use of the Rolls]].) For local travel, the boys ride their bicycles or have one of the salvage yard helpers, [[ThoseTwoGuys Hans or Konrad]], drive them in one of the trucks.

Adding to this quasi-realism was the real-life movie director, Alfred Hitchcock, who appeared in the original texts of the first thirty titles. His character provided the introductory and closing remarks in each book and, acting as a mentor, he was occasionally called upon by The Three Investigators during the course of solving a mystery. The real Alfred Hitchcock had little to do with the creation of these books. He was simply paid a handsome percentage for the use of his name and character. This provided brand-name recognition and helped boost sales of the books.

Following Robert Arthur's death, the writing of the series was taken over by several successive authors — two titles by Nick West (pseudonym of Creator/KinPlatt), three by Creator/MarcBrandel, and the bulk of them penned by William Arden (pseudonym of Creator/DennisLynds) and Creator/MVCarey.

The long-standing popularity of the series in Germany has resulted in two live-action movies, ''The Three Investigators and the Secret of Skeleton Island'' and ''The Three Investigators and the Secret of Terror Castle''.
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!!''The Three Investigators'' provides examples of:

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[[folder: Tropes A-C]]
* AbsurdlySpaciousSewer: ''The Mystery of the Silver Spider'' had the young heroes escape the villains in the storm drain system of a very old city. They meet up with some allies ''rowing a boat through the drain''.
* AchillesHeel / LogicalWeakness:
** By {{Irony}}, the very thing the Investigators need to get around Southern California, the Rolls-Royce, is also so conspicuous it allows the villains (and Skinny Norris) to know what they're doing and where they've been, as they discover right away in ''Stuttering Parrot'' and again in ''Fiery Eye''. They also discover that the Ghost-to-Ghost Hookup, while it allows them to learn information quickly, draws attention to itself too and can allow people they don't want to know about it (like Skinny) to be tipped off thanks to a friend of a friend. The issue with the Rolls-Royce is dealt with by using the car as a decoy on several occasions while they go to their real destination in one of the salvage yard trucks (although this solution and the problem it addressed never came up again in later books, except once when Worthington uses his own car to follow the fellowship to Torrente Canyon in ''Singing Serpent''). The Ghost-to-Ghost Hookup problem quietly vanishes altogether, although it isn't used in many of the books after Arthur's death.
** The junk piled all over the junkyard and especially around Headquarters turns out to be this early on, once the boys realize that while it keeps anyone (especially Aunt Mathilda) from seeing them, it also keeps them from seeing out. Rectified by the invention of the See-All, but it comes up as an important plot point in ''Deadly Double'' when [[spoiler:Ian Carew is hiding in the junkyard from his kidnappers, since it keeps the trio from finding him, too]].
* ActionPrologue: Unusually, this occurs to some degree in ''Wandering Cave Man'', where Jupe encounters a strange pair of travelers in the fog near the junkyard, tries to help them get to where they're going...and then the male traveler has a heart attack and dies, requiring an ambulance be called. This is the first on-screen human death in the series, and it leaves an impression on the reader (and in-story, on Jupe). It's also a ChekhovsGun, for while at first it appears to have nothing to do with the story other than to introduce us to Eleanor Hess and the Spicer Foundation, it ends up being the work of Dr. Birkensteen (the man who died) that is at the heart of the case, since [[spoiler:he accidentally discovered a powerful, side-effect-free anesthetic in the course of his work, and it's this which the main villain uses to carry off his theft and ransom scheme via the town's water supply]]. Also, the beginning of ''Scar-Faced Beggar'' involves Bob's encounter with the eponymous character (who nearly gets hit by a car), then a brief ChaseScene, all while a bank robbery is going on (though this isn't learned by the characters until the next chapter). A few other books had this too, such as ''Stuttering Parrot'' (the first encounter with Claudius), ''Green Ghost'' (Bob and Pete's very atmospheric visit to Matthias Green's ruined mansion), ''Shrinking House'' (the pursuit of the figure in black from the cottage to the barranca), and ''Magic Circle'' (the boys being trapped in the fire at Amigos Press).
* AddedAlliterativeAppeal: A favorite of the book titles, as in ''Green Ghost, Silver Spider, Crooked Cat, Flaming Footprints, Singing Serpent, Monster Mountain, Dancing Devil, Headless Horse, Deadly Double, Sinister Scarecrow, Purple Pirate, Missing Mermaid, Trail of Terror, Rogues' Reunion, Creep-Show Crooks, Wrecker's Rock, Cranky Collector, Dancing Dinosaur, House of Horrors'' and ''Savage Statue''. By the early '80s, alliterative titles were almost obligatory, before being dropped for the ''Crimebusters'' re-launch.
** Also, Jupiter Jones, Liz Logan, the Great Gulliver, Maximilian the Mystic, Sarah Sandow, Doc Dawson, Java Jim, Francesca Fontaine, Miss Maureen Melody, Luther Lomax, and AntiVillain Claude Claudius. And the Verdant Valley Vineyard.
* AdultFear:
** Although the boys get in danger a number of times and often worry their families, ''Deadly Double'' has the most sobering and unsettling example of this when Jupiter is kidnapped not once, but twice...and not only Bob and Pete but Worthington, Chief Reynolds, Uncle Titus, and Aunt Mathilda have to worry about international political extremists and whether they will ever see him alive again (because HeKnowsTooMuch). It is handled quite seriously and realistically throughout the book, making it one of the better and more tense entries in the series.
** A brief moment in ''Shrinking House'', when Skinny has been kidnapped [[spoiler:by Marechal]]. Although she at first confronts Maxwell James and Pete, thinking they have something to do with it, Mrs. Norris's worry and fear for her son are played out quite realistically, even as she acknowledges Skinny's failings and what she didn't know about his doings. It's enough to make even the boys feel sorry for him and want to help save him. (It's also the only time we ever meet her in the series, and she is nothing like his father, so the moment is memorable and telling.)
** Regina Stratten in ''Missing Mermaid''. Not only does her little five-year-old boy disappear twice, but the second disappearance involves his trusted canine companion being found dead in a trash bin, followed by days of being hounded by the press while she worries where he might be, who might have him, and why. How close he came to being eliminated by [[spoiler:Clark Burton]] and the fact he was eventually found in the company of a simple-minded vagrant (albeit completely harmless) doesn't help either.
* AesopAmnesia: Several times (for example, in ''Shrinking House'' and ''Dead Man's Riddle'') Skinny Norris receives a bad scare/brush with danger and death that seems to convince him of the error of his ways. But in the next book he's always back at it again, jealously pursuing and competing with the Investigators, until finally being PutOnABus (and ''maybe'' having a HeelFaceTurn) in ''Headless Horse''.
* AffablyEvil: Hugenay.
-->'''Hugenay''': Ah, Claude. Fancy meeting you here. America isn't such a large place after all.
-->'''Hugenay''': This is the gentleman you met a little while ago in a picturesque spot in Merita Valley.
* AllAsiansKnowMartialArts: Pete amusingly thinks this of Kyoto in ''Two-Toed Pigeon'' when worrying about what will happen to him should the Japanese catch on to his stalling trick.
* AllGirlsLikePonies: Allie and her Appaloosa, Queenie. She actually does serve a purpose in the story in ''Singing Serpent'', however, as her oat bin is where Allie hides the diamond necklace and Pete uses her to trample and capture Shaitan at the climax.
* AllThatGlitters: The novels contained versions of this periodically. One that comes to mind lacked a clear moral: A sunken riverboat holding a watertight chest contained millions of dollars—in worthless Confederate money. It may have been worthless when the book was written, anyway. But these days, preserved Confederate money is worth more than US currency of the same denomination, with mint-condition bills of $100 and $500 worth tens of thousands of dollars. The real irony, of course, is that Confederate money is so valuable now due to most of it being destroyed precisely ''because'' it was considered worthless.
* AmoralAttorney: [[spoiler:Roger Callow]] of ''Dead Man's Riddle''.
* AmusementParkOfDoom: Two have appeared in the series, and both quite memorable. The first, on Skeleton Island, was the site for Pete's dad's film shoot--one which [[ExploitedTrope took advantage]] of this trope by using the amusement park as the setting for the film's climactic fight with the villain. The villains of the book ''also'' made use of the trope by drawing on the park's legendary haunting to keep anyone from finding their hidden bank robbery loot. The second amusement park, in ''Crooked Cat'', served mostly as a set piece for chase scenes, as well as some of the more creepy, suspenseful moments in the book, and also acted as a ready source of hiding places, red herrings, and escapes for the villain.
* AntiVillain: A number of the boys' enemies turn out to be this, either having sympathetic reasons for doing what they do, not genuinely wishing to hurt anyone, being ForcedIntoEvil, performing a HeelFaceTurn, or simply being too AffablyEvil to be hated. Good examples are Mr. Claudius of ''Stuttering Parrot'', [[spoiler:Professor Freeman]] of ''Whispering Mummy'', Arthur Shelby of ''Coughing Dragon'', [[spoiler:Professor Shay]] of ''Phantom Lake'', Señor Santora of ''Haunted Mirror'', [[spoiler:Mrs. Chumley]] of ''Sinister Scarecrow'', [[spoiler:Eleanor Hess and Dr. Hoffer]] of ''Wandering Cave Man'', [[spoiler:Paul Donner]] of ''Kidnapped Whale'', and [[spoiler:Luther Lomax]] of ''Rogues' Reunion''.
* ArchEnemy: That perennial ne'er-do-well Skinny Norris. Later, when Skinny Norris had a HeelFaceTurn, the position was taken by the mastermind Victor Hugenay.
* [[AuthorAvatar Artist Avatar]]: Sort of. When the characters of Bentley and Allie were introduced in ''Singing Serpent'', the illustrator based the looks of the latter off his own daughter and the former off of himself.
* AssholeVictim:
** Charles Barron of ''Blazing Cliffs'', who resents the government, supposedly lazy kids, anyone he thinks does poorly at their job (especially in the service industry), banks, communists...pretty much the entire world, really, to the point his default state is angry. By the time he has badly mistreated the boys, Uncle Titus, and poor Hans, the reader can practically [[RootingForTheEmpire root for the villains to succeed in bilking him out of his fortune]]. By the end of the story he does lighten up, slightly, in seeing he was wrong about the investigators, but otherwise he hasn't seemed to really have learned his lesson.
** Also, Newt and Thalia [=McAfee=] of ''Wandering Cave Man''. Not only are they unfairly (and completely without justification) superior toward Eleanor, acting as if she thinks she's above herself just because she wants to go to college (and her aunt had specifically resented her sister, Eleanor's mother, for being beautiful and making something of herself with an education), they are actively robbing her of both the insurance she was owed after her parents' accident and her inheritance in the form of a house in Hollywood and its rent...so she never has enough money to live on and is forced to stay with them, all while being guilted for how much she supposedly costs. As if that isn't enough, the pair are greedy in other ways, charging far too much money for rent on their property when the town is full of tourists for the cave man, and it's very clear in how Newt acts toward Dr. Brandon that he has no respect for anthropology, only wanting to create a sensationalist story so he can bilk all the people who come to see his kitschy tourist trap. It's no wonder Eleanor decides to [[spoiler:help rob and blackmail them]]. [[note]]The unfortunate thing is that while she does manage to obtain her freedom, money, and a place of her own (after giving them an awesome ReasonYouSuckSpeech), and the cave man is temporarily held as evidence by the police, it isn't made clear if the [=McAfees=] will ever truly pay for their crimes. If Brandon has his way, the governor will ensure they can't claim the fossils and he will instead be allowed to study them, keeping them from becoming a money-making scheme, but we don't know for sure, and because she succeeds in getting her money and a place of her own, Eleanor doesn't press charges against them.[[/note]] Bob mentions his mother's wisdom that people like the [=McAfees=] eventually [[LaserGuidedKarma get what's coming to them]] and make themselves miserable, but to a certain extent they do remain {{Karma Houdini}}s. Also, [[ArsonMurderAndJaywalking Newt annoyingly insists on]] [[ItIsPronouncedTroPay correcting people on their name's pronunciation]].
** Jeremy Pilcher of ''Cranky Collector''. Aside from simply being a nasty, vindictive, suspicious, and insulting old man, as well as something of a miser, it becomes clear from the number of people who hate him and what he has done to them or their friends and relatives in the past that Pilcher is a rather crooked and unethical businessman. There's also the way he treats his daughter as well as the hired help (including the boys) and that the reason for his kidnapping turns out to revolve around a secret South American emerald mine he used to supplement his income whenever money was scarce (after leaving his former partner in the scheme to take the fall for his theft of the antique book that revealed its location--the man was a thief and dangerous criminal himself, but this was still a rather selfish thing to do). This last is particularly noteworthy since despite this criminal activity, Pilcher [[KarmaHoudini gets off scot-free]] at the end, partly due to having been a kidnap victim, partly because the mine in question is no longer his but now worked openly by a legitimate business.
* AuthorAppeal:
** M.V. Carey, a later author in the series, seems to have had a fixation on the supernatural since it figures prominently in at least four of the titles she wrote: ''Singing Serpent'', ''Invisible Dog'', ''Haunted Mirror'', and ''Magic Circle''. She also wrote stories involving cryptozoology and [[FlyingSaucer UFO]] sightings (''Monster Mountain'' and ''Blazing Cliffs'', respectively). Even ''Flaming Footprints'' and ''Sinister Scarecrow'' had vaguely supernatural elements, although the "ghost" leaving footprints and walking scarecrow were just done with [[ScoobyDooHoax chemicals and a costume]]. She also seems to have a thing for small countries with bloody revolutions in either their past or present, since this appears as the backstory in ''Flaming Footprints''; something one of the well-meaning antagonists wants to prevent in ''Haunted Mirror''; and something the villains are actually trying to bring about in ''Scar-Faced Beggar''.
** William Arden, meanwhile, seemed to have a thing for villains who wore costumes or disguises, since this appeared in his very first entry in the series (''Moaning Cave'') and continued in ''Crooked Cat'' (a double disguise, even!), ''Phantom Lake'', ''Dancing Devil'', and ''Purple Pirate'', and even had brief appearances in ''Shrinking House'', ''Shark Reef'', and ''Smashing Glass''.
* AuthorAvatar:
** WordOfGod reveals that Robert Arthur saw much of himself in Bob Andrews and often wrote his traits into the character. Bob was also more often the POV character in Arthur's books than Pete and Jupe were.
** In ''Shark Reef'', the character of John Crowe is named after one of William Arden's other pseudonyms, and like him he is a mystery writer. The physical description also does sound a great deal like his real-life appearance.
* BadassBoast: From the costumed Dancing Devil villain: "We are one, and we are all! We see all, know all! We are the blue sky, the golden sun, the endless steppe, the sword, and the corn! We destroy in the flame of the wind."
* BadGuyBar: Unusually, a form of this appears in ''Shark Reef'' when Bob follows the Connors brothers from the marina; although the tavern in question is not actually a place for villains to gather, it is certainly dark, unpleasant, rowdy, and dangerous, and it ends up being where several villains meet. It's certainly the first time such a place has ever been seen in the series, making it notable in any case.
* BananaRepublic: Ruffino of ''Haunted Mirror'' is basically described as this, a former Spanish colony that became an independent democracy via a [[VelvetRevolution bloodless revolution]].
* BankRobbery: The books which aren't looking for BuriedTreasure, lost masterpieces, or solving puzzles/riddles are usually this, or involve looking for the loot from one that had been hidden. Examples of actual robberies: ''Vanishing Treasure'' (which actually takes up so much of the narrative it's practically a [[HeistFilm Heist Book]]), ''Coughing Dragon'', ''Sinister Scarecrow'' (variation — a museum robbery); finding the loot: ''Skeleton Island'', ''Talking Skull'', ''Crooked Cat'', ''Death Trap Mine'', and ''Scar-Faced Beggar'' (although the bank robbery is only part of the criminal activity going on in the last one).
* BattleButler: Worthington, on occasion. He certainly acts as this in the very first book, even abandoning the Rolls-Royce to help Bob rescue Jupe and Pete inside Terror Castle.
* BeneathSuspicion: Because of their size, [[spoiler:the midgets]] from ''Vanishing Treasure'' are able to disguise themselves as Cub Scouts and are thus never suspected of the robbery until [[spoiler:[[SpottingTheThread one is given away by his gold tooth]]]].
** Usually averted otherwise throughout the series, in fact as often as not it is defied by Jupiter who often ''suspects'' or at least does not discount servants and other seemingly irrelevant characters. At least once, though, Jupiter did almost fall prey to the trope when he continually discounted the possibility that [[spoiler:[[ObfuscatingDisability Mrs. Chumley]] could be the scarecrow]], and he also overlooked [[spoiler:Doc Dawson]] in ''Nervous Lion'' until almost the last minute when a ContrivedCoincidence allowed him to discover the smugglers' coded message [[spoiler:in his medical bag]].
** A different sort of example occurs in ''Rogues' Reunion'' in that because no one would suspect someone in his position (but at the same time it's far too easy for the studio people to overlook someone of his race in that position), he never used his real name when acting, and he no longer does his hair the same way or uses a singsong voice, no one but Jupe realizes that his chauffeur Gordon Harker is [[spoiler:the missing Rogue, Flapjack]].
* BerserkButton: Don't mention to Jupiter that he's fat.
** IAmBigBoned: See above. Jupe has always been a pudgy kid, and is touchy about it.
* BewareTheNiceOnes: Quite often, the obviously nasty, resentful, or suspicious character among the suspects in a case is not the hidden villain, but instead it's the nicest, most unobtrusive, even helpful character the reader thinks is completely trustworthy. Played with however in that also often the mean character still is guilty of ''something'' (whether a lesser crime or some other dark secret), just not for the case at hand.
** Played with in ''Purple Pirate''. [[spoiler:Joshua Evans]] at first seems like the typical sort of nasty character the boys tend to encounter, which makes him seem like the likely villain. Then once he finds out what is going on at the Purple Pirate Lair, he calms down, becomes as friendly and helpful as can be, and does all he can to help them catch the villains. But in the end he turns out to actually be one of the bad guys after all, pitting the boys, Captain Joy, and his former comrades against each other so he can escape with the loot.
* BigfootSasquatchAndYeti: The creature of ''Monster Mountain''.
* BilingualBonus: Appears on occasion, such as Salsipuedes Street in ''Dead Man's Riddle'' meaning "get out if you can", something which a resident of many California towns (or native Spanish speakers) would get right away.
* {{Blackmail}}:
** The source of the plot in ''Haunted Mirror'' — ConMan Diego Manolos was able to use the [[MagicMirror Chiavo glass]] to perform various robberies and crimes, culminating in framing the future president of Ruffino for thievery. He then kept evidence of this (photographs and news clippings) which he used to threaten the president into giving him money, a fancy house, and a high advisory position in the government, lest he lose the next election in favor of a true dictator who would cause a [[TheRevolutionWillNotBeCivilized terrible uprising]] and much suffering in the republic. Obtaining this evidence (hidden on the mirror) is what lies behind the various attempts by both Gomez and Santora to get the mirror, including the ScoobyDooHoax.
** Also occurs in ''Kidnapped Whale'', where a forger of counterfeit money escaped the law and tried to go straight, but is recognized by the villain of the story and forced to aid him in recovering his lost loot or else be turned in to the authorities. The irony is that in trying to escape the blackmail the forger [[CrimeAfterCrime commits several other crimes]], and while the reveal causes the villain to go to jail for counterfeiting, so does he (subverting WrongfulAccusationInsurance)--though arguably he would find this preferable to either living in fear or being forced to continue aiding in other crimes.
* [[BluffingTheMurderer Bluffing the Criminal]]: Jupiter has done this on several occasions to receive an incriminating confession.
* BoundAndGagged: Lots of examples as it's a staple of the genre, including in the very first book. Particularly memorable examples occur in ''Vanishing Treasure'' and ''Fiery Eye''.
* {{Bowdlerization}}: While amazingly nothing about the YellowPeril Mr. Won is changed or edited out of ''Green Ghost'' (either because he's too integral to the plot or because at the time the book was written such tropes [[invoked]][[ValuesDissonance were still held to be be true]]), the pair of Yaquali in ''Laughing Shadow'' were originally called "dark men" in the text (due to their skin color, of course)...but later editions changed this to either "the men in white" or "the strangers" (including in a chapter title). Presumably this was to avoid unfortunate associations, since for most of the book the boys had thought they were the villains.
* UsefulNotes/BritishEnglish: The puzzle of ''Dead Man's Riddle'' is written entirely in Cockney rhyming slang.
* BunglingInventor: Pete's grandfather is made out to be this at first in ''Trail of Terror'', in that his inventions either never work, don't work as they're supposed to, end up being useless/redundant, or they're just plain silly (a convertible house roof?). The invention he is trying to sell in New York, [[SubvertedTrope however]], turns out to be extremely valuable, worthwhile, and beneficial to mankind (a valve to help make space suits and space travel more safe and efficient, as well as cheaper) and he is thus granted legitimacy, respect, and a lucrative contract by NASA.
* BuriedTreasure: Some of the more memorable entries involve these — ''Stuttering Parrot'', ''Skeleton Island'', ''Fiery Eye'', ''Laughing Shadow'', ''Phantom Lake''. The last one was even PirateBooty.
* TheButlerDidIt:
** At one point in ''Whispering Mummy'', the boys suspect Professor Yarborough's butler Wilkins of being involved in the criminal doings, mostly because: he's in the best position to make the mummy whisper (or lie about not having heard it); was the one most insistent on there being a curse and that the professor should get rid of the mummy; and because he had once been a vaudevillian actor and so could have convincingly feigned shock and a faint as well as, possibly, know ventriloquism. Bob also [[DiscussedTrope mentions the trope by name]]. He of course turns out to be innocent. In a variation, one of the professor's gardeners ''does'' turn out to be behind the various dangers which occur to make it seem as if there is a curse (because he's working for the Libyan family the villain has conned into thinking they are descendants of the mummy), but he still isn't the actual villain, just a patsy.
** Played with in several fun ways in ''Sinister Scarecrow''. [[spoiler:The butler (and cook) did do it, in this case commit a robbery, but were only two among [[EverybodyDidIt many guilty parties]], and they aren't real household servants at all but merely posing as ones they encountered on a plane flight. Jupiter investigates them because he knows better than to [[BeneathSuspicion dismiss the hired help]], but is fooled for a while both because they have references from an English lord (falsified, taken from the real servants they met) and because Mrs. Chumley is helping them maintain their various alibis. And the reason they are posing as servants in the first place (aside from the [[JustifiedTrope justified]] criminal advantages of the position) is, of course, because [[GenreSavvy they are aware of the trope]] and how everyone dismisses it, and are thus [[ExploitedTrope exploiting]] its {{Dead Horse|Trope}} nature.]]
* CharacterTic: Jupiter is known for pinching his lower lip when he is thinking furiously and his brain is about to crack a case.
* CharacterizationMarchesOn: In ''Two-Toed Pigeon'' it is revealed that Pete is very much an animal lover. On the one hand this doesn't exactly contradict his earlier characterization--he was the best horse rider of the group in ''Green Ghost'', was able to calm the lion in ''Crooked Cat'' and admired George in ''Nervous Lion'' once he got to know him better, and of the three boys seems the most likely to feel this way since both Jupe and Bob are more interested in bookish pursuits. On the other hand, it's hard to believe someone who once took in a wandering horse as a pet would be as distrustful and wary around Queenie in ''Singing Serpent'' as he was (though that could have been his feelings for Allie bleeding over); his feelings about caged birds (or birds at all) were nowhere in evidence with Blackbeard and the other parrots in ''Stuttering Parrot'' (though he could have developed these views thanks to those experiences--it's also odd, considering the number of {{Continuity Nod}}s he did, that Brandel didn't mention Blackbeard here); and there was never any evidence of Pete and his family keeping pets (though admittedly he's the boy about whose family life the least is known). And while Brandel set up for this in ''Kidnapped Whale'' through how close Pete and Fluke became, it does still come a little out of nowhere, although it is a welcome way to help differentiate the boys further.
* ChekhovsGun: Many across all the books, a lot of them introduced in casual, one-line references very easy to miss upon first reading. Enough to be a ChekhovsArmory at times. A particularly good one, though, is the Model T from ''Death Trap Mine''. At first it appears it's solely in the story (after having attention conspicuously drawn to it) to help prove something is off about Thurgood (him seeming unaware of or rather vague about the vintage cars he is supposed to be a great collector of, and getting wrong what movie set he had lent a car to and when). But in the end it turns out [[spoiler:to be the place where the BankRobbery loot is hidden]].
* CircusBrat: Andy of ''Crooked Cat'', to his grandmother's chagrin and [[FantasyForbiddingFather extreme disapproval]]. This changes by the end of the story when his value to the carnival and enjoyment of the life there is proven to her (as well as that he's perfectly safe there).
* CircusOfFear: The carnival in ''Crooked Cat'' averts this trope since, other than the numerous accidents plaguing it that make the performers think it's bad luck, the show is quite harmless and enjoyable. The [[AmusementParkOfDoom abandoned amusement park]] next door with its rickety roller coaster, ominous fun house (with a HallOfMirrors, natch), and murky tunnel of love, however…
* ClearTheirName: A big part of the plot of ''Screaming Clock'' is this for Harry's dad; also plays a smaller role with Pico in ''Headless Horse'', Chris in ''Skeleton Island'', Mr. Bonestell in ''Scar-Faced Beggar'', and Paul Jacobs in ''Smashing Glass''.
* ClosedCircle: Carried off rather well in ''Blazing Cliffs'': because of the isolated area where Barron has his ranch, it's easy for the villains to use "Road Closed" signs, stolen military vehicles, military costumes, and arsenal and ammunition to block off and guard the only road in and out; one of the villains is a technical whiz who can block any radio signals in the area (except for [[PhonyNewscast the fake ones]] he wants broadcast); and the other villains, who are trusted members of the staff, can easily cut the phone and power lines and use hidden communication devices to be aware of everything going on on the property so that no one can escape.
* CloudCuckoolander: A number of these appear throughout the series whether as clients, witnesses, or clue bearers. Irma Waggoner from ''Stuttering Parrot'' (who is almost a bird-owning version of the CrazyCatLady), Miss Agawam from ''Vanishing Treasure'', Imogene Taylor from ''Screaming Clock'' (who can't find her spectacles after pushing them up on her forehead), Aunt Pat from ''Singing Serpent'', and Mrs. Darnley from ''Haunted Mirror'' are prime examples. Miss Maureen Melody of ''Two-Toed Pigeon'' is...sweet and kind, but very strange. She also seems unable to understand why her neighbors would not enjoy being next door to grounds filled with birds that sing constantly.
* CoincidentalBroadcast: While the news (past or present) is very much a constant source of information for the boys, whether through Bob's research or stories that are brought to their attention in various ways (usually by Alfred Hitchcock and later Hector Sebastian), a few times it does happen in a coincidental manner and at just the right time for them to save the day.
** The last book Arthur wrote, ''Talking Skull'', involves Bob happening to overhear someone at the library talking about being forced to move from Maple Street due to freeway construction, the librarian mentions a piece in the newspaper about it, and he's able to track it down so they know they have a short time to find the missing bank money before the house it's hidden in is demolished. In ''Death Trap Mine'', Bob again happens to notice an old newspaper with an article about the bank robbery the book revolves around.
** But the worst offender (and which plays the trope painfully straight) is in ''Coughing Dragon'' when Pete turns on a radio he repaired just in time to hear about...the disappearance of five dogs in the nearby town of Seaside. Considering the broadcast barely has any information to give them except that a crime took place, and the next announcement is to go on to world news, it's definitely a case of WorstNewsJudgmentEver and clearly done just to get the boys on the case.
** Another played straight example (but far more realistic and well-executed) appears in ''Scar-Faced Beggar'', where Jupiter turns on the TV he just repaired and receives a detailed news report on a BankRobbery which (it turns out) Bob witnessed the beginning of without being aware of it.
* ColdBloodedTorture: A few of the villains threaten the boys with this while holding them BoundAndGagged, but the most memorable would be [[EvilChancellor Duke Stefan]] in ''Silver Spider'' who actually holds them in a medieval dungeon with all sorts of torture implements and threatens to put them in the Iron Maiden.
* CollidingCriminalConspiracies:
** Classic example in ''Creep-Show Crooks'': the villains of the book, a pair of horror movie aficionados desperate to break into the business as independent producers, decide (after discovering that the importer one of them worked for had a huge stash of hidden money) to commit an audacious robbery--stashing the money inside the stuffed teddy bear banks their boss sold, shipping them to a local furrier, then getting a job at the furrier's to intercept the shipment, thereby gaining the money for their venture. What they didn't know was that said money was laundered drug money which their boss was pursuing to get back from them...and they also didn't realize, because of their ineptitude, how they would be forced to keep committing CrimeAfterCrime to obtain the money, thanks to the other of the pair getting fired before he could receive the shipment. Cue an increasingly desperate series of burglaries.[[labelnote:Summation]]Where they: stole fur coats (as well as the bear shipment) to get their needed funds; found one bear had been given away and broke in again to get client records; repeatedly attempted to break into the client's house to find the bear; committed fraud by lying to desperate young actress Lucille Anderson about their vanity project, again so they could get into the house where the bear was; assaulted and kidnapped her to locate it; broke in to the Jones house and assaulted Aunt Mathilda; and broke into Headquarters to finally obtain it[[/labelnote]] And naturally this segued into UnintentionallyNotoriousCrime, since kidnapping Lucille (as well as drawing attention to themselves with a loud dance party) ended up getting her parents and the boys involved, unraveling their scheme. The sad irony is that all they really wanted was to make a great movie like those they loved, but thanks to [[KarmaHoudini the money launderer skipping the country]] and their lack of knowledge of his clients so they had nothing to give the government to plea bargain with, they end up serving the hard time in his stead.
** An even stronger example is in ''Wreckers' Rock'', where Sam Ragnarson's use of a ScoobyDooHoax to scare his family reunion off the island (so he can dig up the lost gold left there by the ship captain who had nearly drowned their ancestor back during Gold Rush days) [[ContrivedCoincidence ends up taking place at the same time]] [[spoiler:a car salesman who's down on his luck and a pair of fishermen friends are trying to fake his death for InsuranceFraud and help him escape the country]]. Being a disreputable black sheep, Sam greedily decides to blackmail them into letting him join in on the scheme, with his hoax also helping to keep the coast clear for the other men's getaway; unfortunately for him, the car salesman is desperate, the fishermen are hardened criminals, and all of them consider him a liability and [[HeKnowsTooMuch unwanted witness/informant]] whom they are only using, and whom they have every intention of getting rid of permanently [[YouHaveOutlivedYourUsefulness once he is no longer needed]]. Also the other reason the conspiracies collide is the fact the boys' photos of the reunion's mock Viking/Chumash battle happen to catch both Sam with some of the gold and [[spoiler:the supposedly dead car salesman]], necessitating all of them working together to get the pictures.
** Another example where the conspiracies do actually interfere with each other is ''Death Trap Mine'', where Allie's insistence that billionaire Wesley Thurgood is a fraud leads her and the boys to explore the eponymous mine and discover the body of a hold-up gang member. This draws the other members of the gang to town to try and recover their lost bank loot, and the end result of all the investigating is the boys also discovering [[spoiler:that Thurgood really is an impostor, as well a ConMan swindler, stock market speculator, and kidnapper of the only person in town who could have recognized his false identity]].
* ColorCodedCharacters: The three boys each have their own color of chalk to use for marking trails, identifying hideouts or places of importance, or leading searchers when they need help. Jupe's is white, Pete's is blue, and Bob's is green. (Overseas, at least one German reprinting has changed this, however, to be [[EaglelandOsmosis red, white, and blue]].)
** The reason for the change in Germany is the cover design. Among other things Creator/AigaRasch designed a label for the series, with white, red and blue questionmarks. It is an on-going joke between German fans that the order of the colour is wrong, because the colours used in the German books are actually white (Justus/Jupiter), blue (Peter) and red (Bob).
* ColorCodedForYourConvenience: Averted and even subverted for the most part; most of the villains in these stories do not wear black (or have black hair/eyes), and the majority of characters who do turn out to be good guys in the end (Reston in ''Moaning Cave'', the strongman Khan in ''Crooked Cat'', [[spoiler:[=DeGroot=]]] in ''Shrinking House'', Stebbins in ''Phantom Lake''). Some outright invert it ([[spoiler:the Countess and Marechal of ''Shrinking House'' both wear white and have light/silver-colored hair]]; the Yaquali of ''Laughing Shadow ''are dark-skinned and wear white, but turn out to be good guys while [[spoiler:Mr. Harris]] also wears white; the Percivals of ''Dead Man's Riddle'' wear white; [[spoiler:Mr. Burroughs]] of ''Sinister Scarecrow'' wears white while the mysterious watcher wears black). The only times the trope is played straight is with Shaitan and Ariel of ''Singing Serpent'' (and considering they are running a demon-worshipping ScamReligion this is likely an InvokedTrope on their part) and General Kaluk of ''Flaming Footprints'' vs. the Potter (but although Kaluk is harsh and cruel, he ends up being a more complex character than he seems, while the Potter is still holding onto a romanticized view of the past, so this may be a case of the narrative misleading the reader once again as to who is right and wrong). Black-clad El Diablo of ''Moaning Cave'' is a zigzagged example, since depending on POV he was either a good guy (a FolkHero to the Mexican people) or a villain (the American authorities, who were the ones to give him [[TheRedBaron his nickname]] of [[TheDreaded "The Devil"]]), but the one encountered in-story is of course a costume worn by the villain.
* TheCommissionerGordon: Chief Reynolds, from ''Green Ghost'' onwards. Usually he is the helpful and friendly sort, albeit at times a bit exasperated with the boys' tendency to get into trouble and Jupiter's arrogance, but sometimes (mostly under M.V. Carey) he falls into outright TeethClenchedTeamwork; whether this was due to resenting all the cases they solved (thus showing up the Rocky Beach police force's weaknesses and need to depend on them for help) or, again, just because of Jupiter's nosy and cocky nature, was never explained.
* ComplainingAboutRescuesTheyDontLike: Textbook example with Jeremy Pilcher in ''Cranky Collector''. Granted, he had just been nearly crushed in a dilapidated house collapsed by a small earthquake, so he had a right to be agitated and to want out as soon as possible. But considering he had to know it would take rescue crews some time to get in and get him out (especially in a safe manner), his attitude is still rather arrogant and infuriating.
* ConcealingCanvas: In ''The Case of the Weeping Coffin'', the eccentric millionaire's house is littered with these, to the point that the curtain that doesn't conceal a safe is interesting.
* ConMan: A popular villain type. Appears in ''Laughing Shadow'', ''Singing Serpent'', ''Monster Mountain'', ''Death Trap Mine'', ''Magic Circle'', ''Sinister Scarecrow'', ''Purple Pirate'', and ''Creep-Show Crooks''.
* ConnectTheDeaths: Not deaths, but in ''Smashing Glass'' the boys try to solve the mystery initially by determining (via Ghost-to-Ghost Hookup) where all the windows have been smashed over the last few weeks and plotting them with pins on a map of Rocky Beach. At first this tells them nothing except what part of town the crimes are happening in, but once Jupiter has the bright idea of using different colors for different days of the week, the pattern is revealed--all in straight lines down the same streets on a particular night, and all on certain nights of the week only. This does not tell them why the smasher is skipping blocks (until they learn those blocks were where there were police stakeouts) or how he knows to skip them (he's being warned by listening to the police band with his radio and headphones), nor does it tell them why he's doing the smashing, but it does at least give them an M.O. and proves the crimes are neither random nor juvenile vandalism.
* ConservationOfDetail: Just about everything in the books is relevant or becomes a clue. Often even the RedHerring has some connection to the plot underfoot.
* ConspiracyTheorist: {{Deconstructed|Trope}} twice in ''Blazing Cliffs''.
** On the one hand, CrazySurvivalist Charles Barron is so resentful, so sure of his own value as a rich self-sufficient landowner who is the only one who works hard anymore, and so misanthropic that he is easily fooled into thinking there's been a revolution, an invasion (by either another country or aliens), and/or a general breakdown of society; thus he believes all his preparations for going it alone out in the wilderness were justified, and he's just as easily tricked into almost giving up his fortune as part of a supposed evacuation to the stars to avoid TheEndOfTheWorldAsWeKnowIt.
** On the other hand his wife is set up as an equally credulous, NewAge DaydreamBeliever who believes without question the latest works by supposed gurus and alien abductees/communers/interpreters, and specifically is convinced that there is a race of benevolent "rescuer" aliens who will descend to carry the elect of humanity away to their planet, saving them from destruction. [[SubvertedTrope However]], she is actually the ''first'' character (aside from Jupiter) who suggests the flying saucer plot is a hoax (and agrees, when Jupiter points out that many people know about her beliefs, that it'd be very easy for someone to try and manipulate her this way); is very practical and intelligent (she's trained as a nurse and is quite capable of climbing rugged cliffs to go to the outside world for help); and will not accept that the "aliens" are those she believes in (although this is helped by them attacking one ranch hand and the boys, thus proving they are not benevolent). So while her actual beliefs remain unchanged by the end, she's actually far more healthily skeptical than she first appeared.
* ContrivedCoincidence: While these have appeared at various points in the mysteries, an extremely blatant one occurs in ''Two-Toed Pigeon'': after the boys are left with a pigeon a stranger accidentally abandoned with them, they visit a nearby bird sanctuary to see if the owner can identify who in the area might own it; not only is [[OneDegreeOfSeparation the person she tells them could possibly help them one of the pearl-smuggling villains (and who had once employed the stranger they met)]], but immediately after this the sanctuary owner calls them to report the murder of some her birds...because a direct line from the oyster farm to where the other pearl-smuggler lives ''just happens'' to cross the sanctuary, the hawks there are killing the pigeons, and so the villain is in turn killing them to protect his investment. ''Also'', when the boys need a message translated from Japanese by Hector Sebastian's cook Don, he takes it to a Japanese friend in his karate class. Not only does this friend happen to be the one who wrote the message, he's also one of the pearl smugglers.
* ConvenientDecoyCat: A literal example actually occurs in ''Purple Pirate'', when Pete is kept from discovery by Joshua Evans by his own black cat Blackbeard.
* ConveyorBeltODoom: Leading to the junkyard metal shredder in ''Nervous Lion''. [[{{Melodrama}} Yes, they went there]] — but at that time it wasn't a DeadHorseTrope yet and it's actually surprisingly tense.
* ConvictionByContradiction: Happens a few times when Jupiter is unmasking the criminal. However unlike with Literature/EncyclopediaBrown, usually said clue actually does prove there was no way the suspect could have said or done what they claimed and they had no reason to lie or be mistaken. They also almost always confessed, and in several cases this slip-up allowed the boys to find actual hard evidence confirming their guilt. Examples: [[spoiler:Marechal and the Countess]] in ''Shrinking House'', [[spoiler:Shay]] in ''Phantom Lake'', [[spoiler:Jefferson Long]] in ''Magic Circle'', [[spoiler:Mrs. Chumley]] in ''Sinister Scarecrow''.
* CoolCar: The Rolls Royce Jupiter wins for 30 days in the first book. Even comes with its own driver, Worthington.
* CorruptCorporateExecutive: Mr. Hanley, owner of the oil company which built Shark Reef #1, complete with a spiel about caring nothing for the birds and fish, only his profits, that would fit right into the ''[[WesternAnimation/CaptainPlanetAndThePlaneteers Captain Planet]]'' RoguesGallery.
* CouldntFindAPen: The Yaquali boy who threw the statuette with a message for help inside in ''Laughing Shadow'' had to use his own blood to write it. In ''Headless Horse'', the boys at first guess Don Sebastian Alvaro did the same thing while dying in his hidden cave, [[SubvertedTrope but instead]] he used a pot of black paint he had brought with him. This is plot-significant.
* CoverIdentityAnomaly: The "jolly fisherman" Mr. Farrier from ''Flaming Footprints'' falls under suspicion due to this — possessing brand-new equipment and pristine, expensive new clothing… but having a dirty, dusty old car that doesn't at all match the rest of him. [[spoiler:He turns out to be a jewel thief in disguise, who had bought all the new, expensive things with a stolen credit card.]]
* CoversAlwaysLie: Happens from time to time. One example is ''The Mystery of the Invisible Dog'', the cover of which shows the investigators cornered by a large transparent feral dog. The invisible dog in the story? A small ''glass statue'', which they are hired to find. Although said feral dog ''is'' a reference to the Carpathian Hound of legend, which the statue depicts.
** ''Missing Mermaid'' is also quite an egregious example: not only is the eponymous mermaid a statue (and one which has only a minor, if critical, role to the plot at that), while the cover shows an actual mermaid, but it's an incredible bit of GettingCrapPastTheRadar since the mermaid is, as is typical, naked from the waist up...and facing the boys, who are openly staring at her.
* CreepyCemetery: Classic example in the Merita Valley graveyard of ''Stuttering Parrot'' where John Silver hid the stolen painting. Not only is the whole scene in the graveyard tense, suspenseful, and eloquently described, lingering in the reader's mind for a long time afterward, but it was so memorable that illustrations of the scene became the endpapers for the hardcover editions for most of the series' run.
* CubCuesProtectiveParent: Happens briefly in ''Monster Mountain'', when the boys encounter a bear cub. Both Jupe and Pete know what to do to avoid danger, thankfully.
* {{Cult}}: Of the eponymous ''Singing Serpent''; despite (or perhaps even because of) being a ScamReligion, it's actually explored fairly seriously and sympathetically for the victim of it.
* CutLexLuthorACheck: Inverted in ''Wandering Cave Man''--the whole reason [[spoiler:Dr. Hoffer]] becomes a villain is because he's afraid the Spicer Foundation ''won't'' pay him their million dollar grant, instead giving it to one of his colleagues. I.e., he very much does want to use his knowledge and intellect for good (and his detailed speech about allergies and immunities shows exactly how much good he could do for humanity) but he feels no one will help him do so unless he makes them.
[[/folder]]

[[folder: Tropes D-F]]
* DarkerAndEdgier: A lot of the books after Arden and Carey took over the series were a lot more serious and had more far-reaching criminal doings. Carey in particular included things such as bloody revolutions, dictators, and villains determined to gain power in either the present or in backstory in both ''Flaming Footprints'' and ''Haunted Mirror'' (and this is taken far more seriously and grimly than Duke Stefan's conspiracy in ''Silver Spider''); there's even a case of terrorist gunrunning in ''Scar-Faced Beggar'' which is put to an end via a fiery boat explosion. There's also the ScamReligion cult in ''Singing Serpent'' and how it affects Aunt Pat; the slew of crimes in ''Invisible Dog'' including extortion, stock speculation, poisoning, bombing, and a fire; the serious results of finding a dead body in ''Death Trap Mine''; and the boys being caught inside a burning building in ''Magic Circle''. Nick West also has the example of the boys almost getting killed by a panther in ''Nervous Lion'', resulting in it being shot in front of them. One of the strongest examples of the trope is ''Deadly Double'' however, where international politics, kidnapping and blackmail all come into play, Uncle Titus and Aunt Mathilda are put through a very real AdultFear, the author [[ShownTheirWork shows his work]] in how the local, county, state, and federal authorities work together in a kidnapping case, and having the freedom of another country and its indigenous people at stake; Arden does not shy away one bit from revealing the racism and extremism of the villains, or making clear what will happen in Nanda if they succeed, and right up to the last moment it appears they're going to get away across the Mexican border.
* ADayInTheLimelight:
** ''Monster Mountain'' is this for Hans and Konrad, since the story is all about going to the Sierra Nevada town where their cousin Anna runs an inn; because it turns out that [[spoiler:she has been replaced by an impostor who is helping a ConMan swindle Anna out of her money]], they are far more involved in the plot than usual, especially in the climax.
** ''Deadly Double'' is this for Bob and Pete as well; since Jupiter gets kidnapped twice, a great deal of the plot involves the two of them (working with the police, of course) doing everything they can to track down the villains and rescue him. Pete figures out the kidnappers took Jupe over grassy ground where their tracks wouldn't show into the chaparral, while Bob finds the business card and question mark he leaves behind; Pete realizes [[spoiler:Miss Lessing]] is lying to them by catching on to the INeverSaidItWasPoison bit with needing to identify Ian, and realizes there's a hidden basement under the house, while Bob identifies [[spoiler:her]] as the helicopter pilot by the missing earring and that [[spoiler:she]] rushed home because Jupiter was being held there. They also figure out the meaning of Ian's "Djanga's place" clue before Jupiter does. It's not surprising Hitchcock observed they did "more shrewd work than their leader" on this case (although Jupiter did contribute greatly to the plot, particularly Ian's rescue at the end). This is a great example of CharacterDevelopment too, since in early books Jupiter insisted they hone their deductive reasoning skills (and often used pranks and object lessons to teach them); apparently by the later books, these lessons have paid off.
* DeadpanSnarker: At various times all the boys get in on this, but Bob especially seems prone to it in the M.V. Carey books, often of a GenreSavvy nature. (And one time where he actually seems GenreBlind, it's Jupiter who calls him out on it.)
* DependingOnTheWriter:
** The earliest books by the series creator Robert J. Arthur made a strong attempt to differentiate the boys' personalities, as well as showing their different interests and intellect levels, so that depending on the case Bob or Pete might have the clue to crack the case rather than Jupe, and their temperaments and personalities determined what roles they played in the investigation or finding the solution. Later books in the series, however, tended to lose some of this characterization so that, as one fansite put it, it almost didn't matter whether Bob or Pete were in the scene or said a certain line because they had become interchangeable. Who made the most jokes or was the DeadpanSnarker also varied from author to author (and book to book).
** Jupe's being a FormerChildStar factored into a great many of the early cases (unsurprisingly, as they were written by the author who invented that {{Backstory}}), and the subsequent authors tried to include it in their early books too… but eventually this element faded from the series, save for one late attempt by Marc Brandel and another in the Crimebusters series to bring it back.
** Jupe's TeenGenius status also fluctuated, even within the Robert Arthur books, where things one would think he'd have discovered and read about turn out to be something he's never heard of — his error in not recognizing Octavian to be Caesar Augustus is particularly egregious — and things he learned in one case don't carry over to another — discovering that uncut diamonds look just like regular rocks when they come out of the earth in ''Moaning Cave'' somehow escapes his memory when the coded cable message in ''Nervous Lion'' refers to "rocks".
** And Pete, who somehow has knowledge on how to work with trained animals in ''Crooked Cat'' courtesy of his father (how would a movie producer come by such knowledge?), shows no such skill in ''Nervous Lion'' when confronted by George; this is particularly noteworthy since he otherwise does show knowledge he learned from his father when talking about Jay Eastland and watching the filming.
** What is Jupe's CharacterTic for when he's in deep thought? In Arthur's books, it's pinching his lip. In other writers' books, it's chewing his lip.
** Early books hid the nature of the boys' doing from the adults in their lives for the most part--they knew they were detectives, but not their methods or what all they did. But by ''Dead Man's Riddle'' Pete is able to tell his father about the Ghost-to-Ghost Hookup without even blinking (and the dialogue implies he had even told him before this). This could also be a case of CharacterizationMarchesOn, however, since eventually with the sheer number of cases they undertook, the boys couldn't hide it all forever--and in the specific case of the Hookup, they'd do better to tell the adults about it and explain how it worked than leave them in the dark; Jupiter at least would likely have figured out the chances of them interfering by that point were greater if they didn't know than if they did.
* DescriptionCut: After being captured by Rawley and the gnomes in ''Vanishing Treasure'', Jupe and Pete are certain Miss Agawam will call the police once she finds them missing, and they'll be saved. Immediately the next chapter cuts to her finding their empty bedroom, deciding they were scared by the gnomes and fled, and calling her nephew in fear to come pick her up, doing nothing to effect a rescue.
* DetectiveDrama: Of the 'closed mystery' sort.
* TheDogBitesBack: Eleanor Hess of ''Wandering Cave Man'', after too many years of browbeating, shaming abuse, does this with a vengeance when she [[spoiler:joins Frank [=DiStefano=] in robbing and blackmailing the [=McAfees=] of the cave man fossils]]. She still gets a good bite in in the end too, by finally obtaining her independence from them.
* DoingInTheWizard: Played with. Often played straight, but some of the "rational" explanations seem to be extremely far-fetched.
* DownInTheDumps: The Three Investigators headquarters is located in Jupiter's uncle's junkyard.
* DramaticShattering: The climax of ''Screaming Clock'', where the eponymous clock is used to [[spoiler:[[GlassShatteringSound shatter the mirror]] in Hadley's library, thus revealing where the stolen paintings have been hidden]].
* DramaticUnmask: Done with [[spoiler:the Amazing Gabbo]] in ''Crooked Cat''...except the man they think is the criminal is [[SubvertedTrope revealed to be innocent]]. [[spoiler:Until Jupe realizes the man is wearing a [[MultilayerFacade double-disguise]] and his real appearance underneath is Gabbo, the bank robber, ''and'' the tattooed man.]] Between Chief Reynolds saying "let's find out just who this robber is" and the subsequent YouMeddlingKids moment, it rather seems as if William Arden was [[AffectionateParody enjoying poking fun at]] (or doing [[ShoutOut Shout Outs]] to) Franchise/ScoobyDoo.
* DudeWheresMyRespect: Interestingly, two of the {{Anti Villain}}s in ''Wandering Cave Man'' have this as their motivation, albeit for completely different reasons. While [[spoiler:Eleanor Hess]] is only acting out of frustration, despair, and self-loathing after years of abuse, [[spoiler:Dr. Hoffer]] is angry at the fact he views his research, something so very critical to the betterment of humanity and with an immediate and practical application, as [[IgnoredExpert being dismissed]] in favor of that of his colleagues. The end result is both of them becoming TheResenter...and deciding to do something drastic about their lack of recognition and fair treatment.
* DyingClue: A few of the riddles or searches for lost treasure involve one of these. The Chumash Hoard's hiding place in ''Laughing Shadow'' is revealed by the FamousLastWords of Chief Magnus Verde, while the delirious Joshua Cameron of ''Shrinking House'' babbled a message for [[spoiler:Marechal]] about the hiding place of the lost Fortunard. Don Sebastian Alvaro of ''Headless Horse'', dying in a cave after the American deserters hunted him down, left one on the wall next to him that was particularly cryptic, but inspired: "Ashes Dust Rain Ocean", meaning that like everything else in life, the Cortes Sword had gone back to where it began...
* EasyAmnesia: Bob suffers from this in ''Silver Spider'', thanks to a TapOnTheHead causing him to conveniently forget where he hid the spider. Interestingly, when he suffers a second blow to the head later, although he doesn't display the proper side effects from this, he doesn't suddenly get his memory back, either.
* ElaborateUndergroundBase: For teens, anyway. Headquarters has secret entrances, a crime lab, and a private phone line with an answering machine (quite a luxury when the stories were written).
* ElectiveBrokenLanguage: In ''The Secret of Shark Reef'', there is a Japanese gardener named Torao. It turns out that he took on a gardener's job in order to investigate the past of his grandfather; his broken English was part of the act (downplayed example, since he was doing it only temporarily).
* EmbarrassingNickname: Jupiter had a backstory as a FormerChildStar with the stage name ''Baby Fatso''. This becomes even worse for him when the revival of the ''Wee Rogues'' in ''Rogues' Reunion'' causes everyone at school to call him by name, beg him to do the character's lisp, and ask for his autograph with said nickname. At the end of the book, though, he manages to sign it as a favor to Hector Sebastian's cook Don.
* EndangeringNewsBroadcast: Several variations of this occur using newspapers or magazines to reveal the information. The article about Mrs. Banfry's cat in ''Whispering Mummy'' is what leads [[spoiler:Freeman]] to kidnap it for his con of Hamid's family; the article about Matthias Green's mansion being torn down is what prompts an old servant to confess to Mr. Won about the Ghost Pearls in ''Green Ghost''; the announcement of Horatio August's death is what brings Three-Dots from India in ''Fiery Eye''; news of Harry's father's trial is what sends Hugenay to South America after Hadley/Bert Clock in ''Screaming Clock''; the story on Jupiter buying Gulliver's trunk at auction brings a gang of thieves seeking bank robbery loot in ''Talking Skull''; the photo of the Potter in a magazine brings Demetrieff and Kaluk to town in ''Flaming Footprints''; and the news of the sunken submarine's discovery in ''Shark Reef'' brings both Torao and the villain to try and find/destroy its secret, respectively.
* EnemyMine: Less serious than most examples (since other than when he almost runs Bob and Harry off the road, no real harm is aimed at the boys), but Hugenay and the boys do work together in ''Screaming Clock''--in return for [[ClearTheirName proving Harry's father's innocence]] (and rescuing Bob and Harry), the art thief will get to keep the stolen paintings once found. Of course thanks to Pete calling the police, it doesn't work out that way, but Hugenay [[MagnificentBastard still gets to walk away scot-free]]. In the later book ''Death Trap Mine'' there is a minor example--when the bank robbers kidnap Pete and Allie, Thurgood not only tries to rescue them and face off with the bad guys, but he provides every assistance to the police in tracking them down. Of course it is in his best interests to do this since [[spoiler:he's both an imposter and secretly running a "salting" and stock swindle via the mine, and has also kidnapped Mrs. Macomber]].
* EurekaMoment: Quite a few of these throughout the series, either when Jupe manages to put all the clues together and understand their meaning, or when one seemingly irrelevant fact or piece of information gets reported/mentioned off-handedly that supplies the answer.
* EverybodyDidIt: Or at least, everyone except [[spoiler:Letitia and Dr. Woolley]] in ''Sinister Scarecrow''. Notable in that while [[spoiler:Mrs. Chumley and the Burroughs]] were working together to rob the Mosby Museum (at least, [[{{Blackmail}} eventually]]), [[spoiler:Gerhart Malz's forgery plan]] was completely separate and had nothing to do with the scarecrow. [[LampshadeHanging As Hitchcock himself says]], "Rarely did the boys have so many suspects turn out to be guilty!"
** Another example occurred two books earlier in ''Magic Circle'': [[spoiler:Harold Thomas/Charles Goodfellow]] turned out to be responsible for both the theft of the manuscript and the films; [[spoiler:Marvin Gray]] was his partner in conning Madeline and gaining the manuscript, while [[spoiler:Jefferson Long]] was the mastermind in ransoming the films. This one is justified in-story by the fact that all three criminals were acquainted before, having been part of Madeline's coterie of actors and film studio workers, as well as her witches' circle.
* EveryoneHatesHades: When one of the thieves in ''Whispering Mummy'' dresses up as Anubis to frighten the butler, the narrative describes him as "the dreaded jackal god". Since this scene is from the POV of the butler however, who is predisposed to view Anubis as evil and frightening, this may just be an in-story invocation of the trope. And considering the thief in question had been told to dress up that way by [[spoiler:someone knowledgeable about ancient Egypt]], it's extremely likely the villain would be aware of the maligning and misunderstanding of a death-related deity and thus was exploiting the trope as well.
* EveryoneIsASuspect: In ''Cranky Collector'', due to everyone at the wedding party for the eponymous collector's daughter having a good reason to hate the victim or want him ruined/mistreated/brought to harm in some fashion, if not physically. Nowhere is this more clear than after his disappearance, when the party guests start openly gossiping and sneering about Pilcher and thinking his fate is well-deserved; the fact he has secret files on everyone who works for him as well as rivals and others he has grudges against only makes the suspect list even greater. It gets to the point that finding out Pilcher's personal secretary is secretly the son of a man he drove out of business actually makes him sympathetic to the boys (and the reader), and no one can blame him when, after assisting in the old man's rescue from his kidnapper and being snapped at and disparaged by Pilcher, the fellow lashes back and refuses to help him any further.
* EvilAllAlong: [[spoiler:The Countess and Marechal from ''Shrinking House'', Professor Shay from ''Phantom Lake'', "Thurgood" from ''Death Trap Mine'', Doc Dawson from ''Nervous Lion'', Professor Walsh from ''Moaning Cave'', Sarah Temple from ''Smashing Glass'', Luther Lomax from ''Rogues' Reunion''...]]
* [[EvilBrit Evil Aussie]]: The villain of ''Laughing Shadow''.
* ExactWords:
** The prize Jupiter won was to have a Rolls Royce at his disposal for 30 days. When one month was nearly over, Jupiter argued that 30 days actually amount to 720 ''hours of service''. The relevant exact words were "30 days of 24 hours each (720 hours), Jupiter argues that by that wording only full days count, and they've only used 3 of them.
** Many riddles and puzzles in the series rely on these, but one of the best is ''Laughing Shadow'': the Chumash chief whose FamousLastWords tell the location of the hoard said "it is in the eye of the sky where no man can find it". [[spoiler:It's hidden ''literally'' in an "eye of the sky", a cave inside a high mountain shaped like an Indian's head, with the cave inside the eye...and it is small enough no man can enter it, but a child or young teen can.]]
** There's also the cryptic words Zelda the Gypsy uses in ''Talking Skull'' when speaking of the fate of the Great Gulliver: "he has left the world of men, and is dead yet alive." [[spoiler:He's FakingTheDead, of course, but he's also [[DisguisedInDrag disguised himself as a woman]]--Zelda herself in fact.]]
* [[ExcitedShowTitle Excited Chapter Title!]]: Every book in the series has at least one chapter title like this, usually more. Invariably it is "Trapped!", "Captured!", or some variation of this where the boys are in some sort of danger. Arden got a bit carried away though in ''Purple Pirate'', which has ''seven'', and ''Dancing Devil'', which has ''eight''.
* {{Expy}}:
** Stephen Terrill is most definitely an {{Expy}} of Lon Chaney, right down to having almost the same nickname (see MasterOfDisguise).
** Based on the names of the characters involved (Kaluk, Demetrieff, Kerenov) and the coup which took place in the {{Backstory}}, the plot of ''Flaming Footprints'' reads like a search for the lost crown jewels of Imperial Russia (or a {{Ruritania}} parallel); note the double-headed eagle symbol of Lapathia was originally used by the Byzantine Empire and then later both Austria-Hungary and Russia.
** A strong case could be made that Jim Hall, Jungle Land, and George of ''Nervous Lion'' are either this or a {{Homage}} to Ralph Helfer, Africa U.S.A., and Zamba.
** The history of the ''Fiery Eye'' dovetails in many ways with that of the Hope Diamond, plus a bit from the famous stolen rubies that jewel thief Klaus Gudden hid in a clay cat statue in 1894.
** Labron Carter and his defunct SinisterSubway beneath Seaside in ''Coughing Dragon'' bear some resemblance to Alfred Ely Beach and the pneumatic transit system he tried to build beneath New York City.
** In ''Deadly Double'', Nanda, the white-dominated former British colony in Africa with a native black population and white nationalist extremists, whose prime minister seeks to be moderate and give everyone equal rights, has more than a few similarities to South Africa. (It plays out as if de Clerk had a teenage son who'd been put in danger to keep him from releasing and making accommodations with Mandela.)
** The disappearance and possible drowning of actress Francesca Fontaine in the backstory for ''Missing Mermaid'' seems like a cross-pollination between the fates of Natalie Wood and Barbara Colby (who actually died mysteriously in Venice itself, several years before the book was published).
** When Marc Brandel finally reveals in ''Rogues' Reunion'' the name and nature of the show on which Jupiter starred as a child actor, it is rather blatantly based on/inspired by ''Our Gang''. Aside from the name mapping perfectly (''The Little Rascals''/''The Wee Rogues''), Jupiter's Baby Fatso and the other characters are extremely reminiscent of the main six children from the shorts' heyday:
*** Flapjack is obviously Buckwheat.
*** Peggy is Darla (in looks, and she also has some of one of the actual Peggys' traits, namely coming to the rescue of/caring for a younger, chubbier character).
*** Footsie is Alfalfa (with big feet instead of big ears).
*** Bonehead is Butch (who for quite some time was rather mean and bullyish toward the others).
*** Jupe is Porky (with a few elements of Joe Cobb thrown in like being much younger than the others, but he definitely has a speech impediment that affects all his lines rather than just one CatchPhrase, he's the butt of a lot of jokes, and Jupe specifically points out the [[HeterosexualLifePartners close friendship]] he (and his character) had with the Buckwheat stand-in).
*** The only one without a direct parallel, Bloodhound, does end up growing up to become a businessman, something which also happened to the actor who played Spanky. The main director of the early shorts, Robert [=McGowan=], also has a few similarities to the fictional Luther Lomax who directed the ''Wee Rogues''. The main difference of, course, is there being only this small cast instead of a constantly changing roster as actors grew up; the actors are also all still alive, but as the story takes place when they are young adults, there thankfully isn't an opportunity yet for any kind of "death curse" to occur.
* FakingTheDead: [[spoiler:Stephen Terrill. Complete with LivingADoubleLife and a SecretIdentity, with the assistance of Charles Grant as his SecretKeeper.]]
* FakinMacGuffin: In ''Phantom Lake'', Java Jim wants a journal that the boys have which was written in the mid 1800s, with potential clues to a BuriedTreasure. Jupiter hands it over, then after Jim leaves [[StolenMacguffinReveal he reveals that he only gave up the oilskin cover of the journal]], having taken the pages out first. He also pulls a similar trick on [[spoiler:Marechal]] in ''Shrinking House'', switching the lost Fortunard for a piece of blank awning canvas.
** Also happens a few times with a hidden treasure when the riddle/puzzlemaker is particularly clever (or trollish). ''Fiery Eye'' and ''Dead Man's Riddle'' are the most notable. (The ''Fiery Eye'' example also involves Jupiter, again, giving the fake version to the villains after having been fooled himself earlier.)
* FauxHorrific: "You must be prepared, in this new adventure...to face a horror that makes even ''my'' blood run cold! I shudder at the very thought of it. What, can there truly be more than one...? But no, I cannot speak the dread words! ...I will not speak of the unexpected fact that lies at the heart of the adventure! It is too monstrous to think of!" [[spoiler:This is Hitchcock in his introduction to ''Deadly Double'', speaking of there being two Jupiter Joneses in the world.]]
* FolkHero: El Diablo of ''Moaning Cave''. Explicitly compared to RobinHood in-story, he was a young Spanish nobleman whose family lands had been stolen, lost, or given away thanks to the influx of Californian settlers and, seeing the Americans as usurpers and thieves, turned into an outlaw to rob the government and drive them out. Though the Spanish peasantry saw him as a defender of justice and righter of wrongs, he was caught, arrested, tried, and about to be executed until freed by some of his friends, allowing him to escape (though badly wounded) to his cave hideout. There he was chased and surrounded by the authorities but never emerged, because he believed it was BetterToDieThanBeKilled. He even became a literal KingInTheMountain, as after his death the legends persisted that he was still alive, whether hiding in the cave or having escaped by some secret means, and would return one day to help his people when the need was greatest.
* {{Foreshadowing}}: The series isn't exactly known for this, but it does occur in ''Silver Spider'': when searching their room for the missing jewelry, the boys see a cricket become ensnared in a web, and then only a scant few minutes later all of them except Pete and Elena get captured by Duke Stefan's guards. The subtlety is unfortunately undercut by Pete [[DiscussedTrope actually commenting on it]], [[TemptingFate hoping it wasn't a sign of bad luck for them]]. However, later in their cell when they break free with a TheGuardsMustBeCrazy plot, Rudy observes that the guards tied up in their blanket-nooses are struggling just like the cricket, suggesting if there was an omen it wasn't just a bad one after all.
* FormerChildStar: Jupiter as a very young child, known as "[[EmbarrassingNickname Baby Fatso]]". While this generally gives him knowledge of show business and acting that comes in handy in various cases, it particularly allows him to be useful in ''Crooked Cat'', since it extends to knowing much about circus and carnival life. He even gets to perform as a clown, albeit out of desperation, during the climax. The show he was once a part of also gets featured in a couple of cases, ''The Mystery of the Rogues' Reunion'' and one in the Crimebusters series.
* {{Frameup}}: Happens fairly often, such as: Harry's father in ''Screaming Clock'', Hank Morton in ''Nervous Lion'', Stebbins in ''Phantom Lake'', Pico in ''Headless Horse''. It also happened once to the Investigators themselves, when the silver spider of Varania is planted in their room to blame them for its theft as part of Duke Stefan's conspiracy.
* FreshClue: In ''The Secret of Phantom Lake'', Jupiter Jones realizes that the perp hadn't just pulled up and tried to help because his car hood is cold and the ground underneath it is dry. (They're in the middle of a downpour.) This proves that the perp had been there for quite some time digging up a BuriedTreasure.
* FriendlyEnemy: Hugenay again.
[[/folder]]

[[folder: Tropes G-I]]
* {{Gaslighting}}: While the intent was only to distract her or force her to leave the estate so the museum robbery could go off as planned, the exploitation of Letitia Radford's fear of scarecrows and bugs in ''Sinister Scarecrow'' is malicious enough to count as this trope, and she nearly does go mad. Ends up being subverted, however, when the villains' concern that the boys will catch on to their scheme leads to the scarecrow attacking the boys, thus proving it isn't just in Letitia's head.
* GameBetweenHeirs: Variation. The eponymous ''Dead Man's Riddle'' does allow a competition between Dingo Towne's family members to find his hidden jewels, but because he hated most of them and distrusted or misjudged the rest, he opened the game to any random person in town who could solve it.
* GeneticEngineeringIsTheNewNuke: Aunt Mathilda's reaction to learning of Dr. Birkensteen's work in enhancing animal intellgence in ''Wandering Cave Man'' makes it very clear she ascribes to this trope.
* GenreSavvy: In the Crime Busters book ''Funny Business'' the Investigators' [[MsFanservice newest ally]] distracts a crowd so that the team can sneak into a secured area. Unfortunately, the only person who is NotDistractedByTheSexy is the one person who needed to not be watching as they snuck in. He even [[LampshadeHanging comments on how obvious their plan was]] after he captures them.
* GetRichQuickScheme: The villain in ''Smashing Glass'' is attempting one of these via a very simple con--breaking windows of cars all over town because he happens to work as a new sales manager at the only glass store in town which replaces windows for every make of car. Ironically, the second, hidden villain is doing the same thing by piggybacking on his plan [[spoiler:stealing her own uncle's rare coin to sell, and using the broken window to make it seem the first villain is who stole it]].
* GettingCrapPastTheRadar: In keeping with M.V. Carey making her entries in the series more adult, there's a moment in ''Missing Mermaid'' where Mrs. Peabody is discussing Mooch Henderson and his house of vagrants, and it seems very clear she was about to claim one of them is a loose woman (i.e. a slut). Also, the fact the story takes place in Venice, California, at the height of its infamous carnival, and some of the people and activities which take place there, is certainly pushing the envelope of what usually occurs in these books.
* GhostTown: The former mining town Powder Gulch is featured fairly prominently in ''Phantom Lake'' as a place visited by Angus Gunn when preparing his wife's surprise (and treasure-hiding place). Another, Hambone, appears briefly (but still as a plot point) in ''Death Trap Mine''.
* GlassShatteringSound:
** The purpose of [[spoiler:the screaming clock]], as inspired by the trick professional screamer [[spoiler:Bert Clock]] used to like doing for his friends.
** Bob and Pete consider this as a possible explanation for the eponymous ''Smashing Glass'', but it turns out to be something much more prosaic.
* [[GoodLawyersGoodClients Good Detectives, Good Clients]]: Played utterly straight for almost every book in the series, with the boys' clients either being innocent victims of the con men/robbers/kidnappers, or bystanders caught up in such schemes by being in the wrong place at the wrong time or stumbling upon an important PlotCoupon. Which is why the subversion [[spoiler:in ''Shrinking House'' where both [[BeautyEqualsGoodness the elegant Marechal and the beautiful Countess]] turn out to be the swindling bad guys, the [[DarkIsNotEvil seemingly villainous]] [=DeGroot=] is actually a Dutch cop in pursuit of them, and Joshua Cameron himself was a master forger]] is so shocking and one of the most memorable entries in the whole series. Subverted again in [[spoiler:''Dancing Devil'']] but with less fanfare. ''Rogues' Reunion'' also subverts it, but the trope is still played with in that the villainous client in question is fairly sympathetic as well as not right in the head.
* GoodScarsEvilScars:
** Played with for the Whisperer of ''Terror Castle''--although his scar is ugly, vicious-looking, and disturbing, he himself is as good-hearted and friendly as can be. On the other hand, [[InvokedTrope the whole reason Stephen Terrill had him as his manager]] was because he ''looked'' sinister, making people afraid to go against him and thus leave Terrill in peace/give him what he wanted. [[spoiler:Subverted in the end since the Whisperer ''is'' Terrill and the scar itself is fake.]]
** Subverted in ''Moaning Cave'', where Reston's scar is just a fake he wears as part of his disguise to fool Laslo Schmidt and, after being played up as a villain for most of the book, he turns out to be a detective for the stolen diamonds' insurance company.
* GoshDangItToHeck: Goes with the genre, although the UnusualEuphemism used by Aunt Mathilda ("Mercy and goodness and sweetness and light!") stands out. A very notable example however is from ''Green Ghost''--Chief Reynolds to Bob's reporter father, when he asked if he could quote him on having seen the eponymous green ghost: "You know darned well you can't!" On the one hand, this is in front of the boys; on the other hand, it's hard to imagine a police chief, even in a small town, not having saucier language than this. By contrast, as proof of [[CasanovaWannabe how smarmy Farrier is for his putting the moves on Mrs. Dobson]], ''Flaming Footprints'' has a subversion from Aunt Mathilda where she calls him a "silly ass!"
** In ''Shark Reef'' one of the protest group's chants (complete with a SloganYellingMegaphoneGuy) is, amusingly, the famous but {{Bowdlerize}}d, "Heck, no, we won't go!"
** NarrativeProfanityFilter:
*** The mynah bird Blackbeard from ''Stuttering Parrot'' was taught a number of racy pirate slang and swear words "not meant for decent company" according to the old lady who bought him. When the boys first get to hear him speak, the text notes he "burst into a string of expressions the boys knew their families would never approve of".
*** In ''Screaming Clock'', when told of Jeeters, Carlos, and Jerry having kidnapped Bob and Harry, Hugenay "let out several expressive words in French." (You can bet ''merde'' was one of them.) A similar thing happens from Carlos only with Spanish when the "cops" burst in to arrest them.
* {{Gossipy Hen|s}}: Mrs. Peabody of ''Missing Mermaid''. Although it is undeniably true that much of what she says has a basis in fact (and she turns out to be absolutely right about both Mooch Henderson and Clark Burton), the ways in which she spies upon and sits in judgment of those around her, and ruins their lives if she deems them enemies or beneath her incredibly high moral standards, is both nasty and unsettling.
* GracefulLoser: Several of the baddies, but Mr. Won of ''Green Ghost'' (who returns the deed to Verdant Valley despite the Ghost Pearls being destroyed) and Hugenay in ''Stuttering Parrot'' stand out. The latter even calls the boys to congratulate them and tip them off to having gained the treasure.
* HalfwayPlotSwitch: Happens on occasion.
** ''Vanishing Treasure'': A case about a stolen belt, and then one about a lady being haunted by gnomes, turns into a bank robbery case.
** ''Monster Mountain'': A case about a missing key turns into a sasquatch hunt, then [[spoiler:a race to rescue a kidnapped woman who'd been replaced by an imposter]].
** ''Dancing Devil'': A case about a bunch of missing black cases becomes one about the missing statue of the title.
** ''Sinister Scarecrow'': A case about helping a [[{{Gaslighting}} traumatized]] and [[ProperlyParanoid paranoid]] woman afraid of ants turns into preventing a museum robbery.
** In an interesting inversion from ''Vanishing Treasure'', ''Scar-Faced Beggar'' starts out as a bank robbery case (and exonerating an old night watchman) but turns into stopping gunrunners for a patriotic (but bloody) rebellion in South America.
** The eponymous ''Kidnapped Whale'' is found almost immediately; the rest of the book deals with trying to help an AntiVillain strong-armed into using the mammal to find a lost cashbox underwater while exposing the villains involved.
** ''Rogues' Reunion'': A case involving winning a rigged quiz show and discovering who stole the valuable silver cups meant to be prizes for the participants turns into rescuing a kidnap victim from [[spoiler:an insane Hollywood director]].
* HandicappedBadass: For the first three books of the series, Bob wears a leg brace due to multiple fractures he suffered after falling down a steep hillside while climbing. The trope is played with in a number of ways, however--while Bob is unquestionably courageous and does not let his injuries keep him from investigating or being of use as many ways as he can, he isn't shown to be badass, not being capable of anything more than the other boys, or any normal person. At the same time he's not InspirationallyDisadvantaged either, nor does anyone ever assume that DisabledMeansHelpless; the only trope he comes close to fulfilling is GeniusCripple due to his intellect, but while he is smart, the real genius of the group is Jupiter. So in the end he manages to be just what he appears to be on the surface--a normal boy who got injured, was temporarily crippled, then healed and became just like his detective partners, a very realistic way of addressing disabilities that is quite refreshing for the time the stories were written. And the fact his injuries were the sort which could heal easily over time suggests it wasn't a case of Robert Arthur initially intending to hew to this trope (or InspirationallyDisadvantaged) and then backpedaling when he realized the UnfortunateImplications--he always intended Bob to get better.
* HauntedCastle: Their first case involved investigating one.
* HaveAGayOldTime: As usual for books written during that era, the word "queer" tends to turn up a lot. There's also an unusual word usage in ''Crooked Cat'' where Andy, during his barker spiel, calls Pete a "nimrod". Considering the fact he was about to compete in a shooting gallery, comparing him to a great historical general makes sense, but thanks to [[WesternAnimation/LooneyTunes Bugs Bunny]] no one in modern times can take that word seriously any more...and so would likely conclude Andy was mocking Pete. Comparing the publication date of the book to those of WesternAnimation/LooneyTunes episodes, it's remotely possible this more modern meaning was actually known at the time, and so its usage there [[InvokedTrope intentionally]] had a double meaning.
* HiddenInPlainSight: A favorite for solving various mysteries. The silver spider turns out to be [[spoiler:in a spider web with a real spider]], the crooked cat was [[spoiler:in the work basket to be repaired]], the crown of Lapathia of ''Flaming Footprints'' was [[spoiler:in an urn by the front door of the Potter's house]], the diamonds in ''Nervous Lion'' were in [[spoiler:the bars of the cages]] they'd had with them all along, the Phantom Lake turned out to be [[spoiler:the man-made "view down the loch" where the treasure was buried]], the invisible dog (a crystal statue) was hidden [[spoiler:in a swimming pool]], the Cortes Sword of ''Headless Horse'' turned out to be [[spoiler:painted and nailed to the side of the Cortes statue]], and Shozo Yamura's ring in ''Shark Reef'' [[spoiler:is on Pete's hand the whole time, covered in mud]].
** It also turns out the reason the kidnappers in ''Deadly Double'' confused Jupiter for Ian Carew, and expected him to be in the area, is because [[spoiler:Ian managed to evade them not far from the salvage yard and had been hiding there under their noses the whole time]]. Foreshadowed by [[spoiler:Pete's missing lunch and the food vanishing from the Joneses' refrigerator]].
* HistoryRepeats: Happens to [[spoiler:Marvin Gray]] of ''Magic Circle'', who gets in a car accident exactly the same way Madeline Bainbridge's boyfriend did thirty years before. Unlike him, he survives.
* HoistByHisOwnPetard: While several villains are brought down by something of their own in {{Iron|y}}ic fashion ([[spoiler:Mr. Harris]] and his kookaburra from ''Laughing Shadow'' and [[spoiler:Professor Walsh]] and his theory of [[spoiler:El Diablo being left-handed]] in ''Moaning Cave'' come to mind), the actual trope only shows up straightforwardly in ''Coughing Dragon.'' First Henry Allen theorizes that whoever created the dragon is giving him a taste of his own medicine, since he used to be a horror film director (specifically one who used a lot of dragons in his work). Then the boys end up deciding to use a film Pete's dad had on hand, [[AttackOfTheFiftyFootWhatever one with giant monster ants]], to scare away the criminals who were themselves using the (fake) dragon to keep people away from the old tunnel. In the end the mastermind behind the scheme is not fooled, but it turns out the reason his doings came to light was because the whistle he used to control the cave's hidden entrance was high enough it attracted all the neighborhood's dogs.
* HostageForMacGuffin: Constantly.
* IdenticalLookingAsians: Bob has a moment where he muses about this in ''Two-Toed Pigeon'' (which is funny, since he never mentioned this when meeting Chang way back in ''Green Ghost'')--but then he immediately backpedals, noting the Asians in question might very well think the same thing about him and the other boys as Caucasians, and works to find distinguishing features so he can avert this. Jupe, naturally, completely averts the trope thanks to his keen powers of observation, and it turns out Bob's thoughts are incredibly prescient, since one of the villains takes advantage of the Japanese Kyoto not being able to tell "short, fat, dark-haired Americans" apart to disguise himself as his partner-in-crime and thus horn in on his pigeon pearl smuggling.
* IdenticalStranger: Jupiter has one in ''Deadly Double'', the son of an African prime minister. [[spoiler:[[ThoseTwoGuys Hans and Konrad]]'s cousin Anna also has one in ''Monster Mountain'', leading to [[KillAndReplace Imprison and Replace]] by her CriminalDoppelganger so that her ConMan husband can steal Anna's money. Foreshadowed by Anna's odd refusal to reply in German when Hans and Konrad speak it to her, although she clearly can understand them. The Identical Stranger is native to Germany but knows an entirely different dialect, so it would be painfully obvious she wasn't actually their cousin]].
* IdenticalTwinIDTag: In ''Deadly Double'', not only do Jupiter and Ian Carew look exactly alike (and Ian, being the son of a diplomat and politician, is well-educated and thus has similar speech patterns to Jupiter), but thanks to Ian getting his clothes damaged and having to steal some of Jupiter's, they even dress alike. The trope even gets played literally straight when the kidnappers try and use an ID tag with Jupiter's name on it to identify which boy is which...except since Ian stole some of Jupiter's clothes, they both have the tags. In the end the only way to tell them apart is to find someone who knows Ian well and can reveal a distinguishing mark: [[spoiler:a scar on his stomach from having his appendix removed]].
* IDontLikeTheSoundOfThatPlace: The Three Investigators seem to keep ending up at places like this: Terror Castle, Skeleton Island, Phantom Lake, Monster Mountain, Death Trap Mine, Shark Reef, Wrecker's Rock...
* ImpersonatingAnOfficer: In ''Screaming Clock'' Hugenay the ClassyCatBurglar has one of his men dress up as a police officer. When the cops show up and try to use that as a charge, he points out that the fake cop is in fact wearing a New York Police uniform (the series is set in California), and as such cannot be accused of impersonating the local police.
* ImposterForgotOneDetail:
** [[spoiler:The con man pretending to be Wesley Thurgood in ''Death Trap Mine'' forgot/didn't know the real Thurgood didn't have blue eyes.]]
** Subverted in ''Rogues' Reunion''--the actor [[spoiler:who impersonates Bonehead]] knows very well that he lacks [[spoiler:the telltale dangling earlobes of the real Bonehead]] and so he covers it up [[spoiler:by growing his hair long and keeping it combed down over his ears]]. DoubleSubverted, however, when Jupiter [[spoiler:takes advantage of a windy day and the actor's tendency to ride in his convertible with the top down to take a picture of him with his secret lapel camera--showing his ears are nothing like the real Bonehead's]].
* INeverSaidItWasPoison:
** In ''Kidnapped Whale'', Constance Carmel blurts out the eponymous whale's species before she could know it. Played with however in that she includes the species in a list ending with "or whatever kind it is" to try and throw the boys off with seeming vagueness--but Bob correctly observes that her inclusion of the right species was too much of a coincidence since it was a rarer species (and he was in fact the only one who had realized what kind of whale Fluke was). Also played with in that despite this, Constance isn't a villain, just [[ForcedIntoEvil forced to aid one]] in order to pay for her smuggler father's hospital bill after his ship sinks.
** On another occasion (in ''Laughing Shadow''), Ted Sandow asks what the "???" on their business card means. This is a OnceAnEpisode thing which wouldn't normally be significant, but Jupe notices that he didn't actually read the card, and must have seen it before. Of course this is also just a RedHerring, as the true villain of the story is [[spoiler:Mr. Harris]], not Ted.
** [[spoiler:Jefferson Long]] of ''Magic Circle'' gave himself away by reporting [[spoiler:the exact number of assailants who stole the films]] before that information was released to the press.
** Senor Santora of ''Haunted Mirror'', when told that a robber had tried to take the Chiavo glass, referred to the robber as a "small man" despite supposedly not having seen him, thus suggesting he did indeed know of the thief. Since any person would seem small next to the mirror, however, this only serves as circumstantial evidence and the boys must track down further clues to determine his guilt or innocence.
** One of the villains in ''Deadly Double'' does this ''twice'': [[spoiler:when Sir Roger's followers realize the kidnappers need someone who knows Ian well so they can identify him, and go to Anna Lessing to find out where her boss and close friend of the family is, she immediately reveals her boss could indeed identify Ian for them...''before'' they get to explain to her why they need to find her boss, thus giving away she was in on the kidnapping (since only the boys, the Nandans, the police, and the kidnappers knew there were two boys who had both been taken and could not be told apart). Then a little later when they confront her at her house and reveal both Ian and Jupiter have been taken, she says she doesn't know who Jupiter is and has no idea where the boys have been taken...revealing she does in fact know him, or else she might have assumed Jupiter was an adult.]]
* IntrepidReporter: Jefferson Long of ''Magic Circle''. [[spoiler:He also turns out to be a FakeUltimateHero, GloryHound, and MilesGloriosus.]]
* {{Irony}}: A number of examples.
** In ''Green Ghost'' Pete hides the Ghost Pearls inside an old burro skull in the mine, thinking they will be safer there (and less easily found) than in the fake flashlight or behind a rock...only to have a minor tremor bring a rock down on the skull, crushing both it and the pearls.
** In ''Talking Skull'' Spike Neely hides his bank robbery loot in a place he thinks is secure and will never change or move, except his sister eventually changes homes, the house is moved to a new address to make room for an apartment building, and ''then'' the house is going to be demolished to make room for a freeway.
** In ''Laughing Shadow'' Jupe tells [[spoiler:Mr. Harris]] all about the laughing shadow, the statue with the hidden message, the two men in white, and the prisoners on the Sandow Estate, not realizing he is the BigBad.
** In ''Crooked Cat'' the villain starts a fire to keep from being caught by the police, but the fire ends up [[spoiler:burning the very cat he hid his left-luggage ticket on, sending it to the work basket for repairs so that no one including himself can find it for most of the book]].
** In ''Flaming Footprints'' everyone is looking for the missing Potter only for him to be hiding right on the very property his enemy Kaluk has been renting, in a room above the garage of Hilltop House no one can see him going in and out of, and the Lapathian crown is hidden [[spoiler:in one of the urns by the front door, right where everyone looking for it walks past it numerous times]].
** In ''Shrinking House'', the Countess claims to have seen [=DeGroot=] [[spoiler:in order to escape with the lost masterpiece]] but he actually is nearby, watching, and chases her.
** In ''Monster Mountain'' the creature Havemeyer is trying to hunt down ends up being what inadvertently helps [[spoiler:free the kidnapped Anna]].
** In ''Death Trap Mine'' [[spoiler:Allie and the boys sit down in the barn to read the newspaper article about the BankRobbery...right next to the Model T where the loot is hidden]].
** In a sadder example, [[spoiler:Mrs. Chumley]] of ''Sinister Scarecrow'' ends up staying quiet about the robbery of the Mosby Museum so she can [[spoiler:get the Vermeer she wanted for so very long...only to get a fake because Gerhart Malz replaced it with a forgery]]. (This also applies to [[spoiler:the Burroughs]] too, committing the robbery for nothing.)
** In ''Shark Reef'', Jupiter tells Bob and Mr. Crowe over the radio about the damage done to the ''Sea Wind'' by the Connors brothers, and warns them to be careful of them...right while they are being held prisoner by the brothers and Yamura, who are sitting right there listening in.
** As Jupiter points out, if [[spoiler:Dr. Hoffer]] of ''Wandering Cave Man'' had simply left well enough alone, he likely would have been given the grant he coveted, but thanks to his actions he is now a pariah in the scientific community and his work, which was genuinely beneficial to mankind, will likely never get the attention or respect it deserves.
** Snabel in ''Trail of Terror'', who has been snooping on his neighbor (Pete's grandfather), is also a spy for a foreign power...and because of this fact plus his guilty conscience, he assumes when Mr. Peck starts loudly proclaiming his identity as a spy and thief that he's referring to the larger conspiracy, not the petty feud, thus pushing Snabel to pursue the group and make them even more suspicious of him. If he hadn't done this (and if he hadn't been so nasty and trouble-making to begin with so as to earn Mr. Peck's enmity), they likely never would have suspected him of anything, and his scheme certainly wouldn't have unraveled--since it's because of Peck assaulting him for supposedly following and spying on him that the camera and its incriminating film gets mistakenly switched with Bob's.
* ItOnlyWorksOnce: Variation--in ''Shrinking House'' the boys are told that people unfamiliar to the area where the case takes place only fall in the barranca on the property once (thus learning it's there and avoiding it in future). This is then used to identify which character is the masked thief (who falls in right near the start of the book) based on whether they fell into the barranca later.
* ItsForABook: Quite often the boys give an excuse like this ("it's for school/a book report/homework/extra credit/we need to make up our grade in summer school") when they are investigating, under the very valid reason that adults will usually either not take them seriously or outright refuse to answer what seems like "dumb kids prying where they aren't wanted"...but the minute school and anything related to it is brought up, all such objections disappear and adults become very cooperative.
* ItsQuietTooQuiet: Done extremely effectively and unnervingly in ''Monster Mountain'' when Bob is searching in the woods and about to come upon the local Bigfoot.
* ItWontTurnOff: In ''Terror Castle'', the boys are told about the cursed OminousPipeOrgan that played both when nobody was near it, and when it was unplugged. (Stephen Terrill supposedly did experiments to be sure.) They later investigate the organ, but it turns out to be just a trick, like everything else in the HauntedHouse.
* IWasJustJoking: Happens a few times when Bob or Pete makes a sarcastic or humorous suggestion, only for Jupiter to have a EurekaMoment thanks to taking it somewhat seriously. Example from ''Headless Horse'', when they're trying to find Condor Castle:
-->'''Pete''': Maybe we need an old Indian map, and an old Indian to read it for us.
-->'''Jupiter''': Pete, I think you've got it!
-->'''Pete''': Gosh, First, it wasn't that bad a joke.
[[/folder]]

[[folder: Tropes J-N]]
* KarmaHoudini: Generally the series is not known for these--either the villain gets sent to jail at the end of the story, or if it's about pursuing a lost fortune/item, they fail to get it and leave at the end--otherwise unpunished for any fell deeds they committed while on the search, but failing to find what they coveted would be punishment enough in their eyes. At least twice though, a villain did actually escape despite the very real crimes they committed--Jensen, Mr. Won's minion in ''Green Ghost'', gets away (as does, for that matter, Mr. Won), while Rawley and his gang escape in ''Vanishing Treasure''. This last is notable not only because of the determined attempt by the boys that the "gnomes" of that case did ''not'' get to be this trope, but because of what Rawley did: he was an exceedingly clever criminal who almost got away with his loot, he coldly threatened Jupe and Pete with [[CementShoes being dumped off a ship with bags of silver coins tied to them]], and while he, like so many kids in the neighborhood growing up, had been one of Miss Agawam's gnomes and came to visit her frequently, he repays her as an adult by using the "gnomes" to frighten her into moving so she wouldn't discover the tunnel being dug under her house. Even though the "gnomes" do get caught, and Miss Agawam moves to a new home with no harm done, that's still a nasty thing to do to such a sweet, harmless person...and yet he still gets away.
* KickTheDog: While a number of villains do terrible things (for a kids' series version of terrible--as usual, none of them ever commit murder that we know of), two which stand out would be the villain of ''Laughing Shadow'' who indulges in child slave labor to find the treasure (and has every intention of either killing them or leaving them to die after he's gained the treasure so as to cover his tracks) and [[spoiler:Mrs. Chumley]] of ''Sinister Scarecrow'' who uses [[spoiler:her]] knowledge of Letitia Radford to create the terrorizing scarecrow; this last is one of the few things keeping [[spoiler:her]] from being a completely sympathetic villain.
* {{Kid Detective}}s: The basic formula.
* LaResistance: The Minstrel Party of Varania, opposing Duke Stefan in ''Silver Spider''.
* LargeHam: No pun intended (remember that BerserkButton), but it's pointed out several times how much Jupiter has a flair for the dramatic and loves hamming it up, usually when unmasking a criminal, solving a riddle, or revealing where the treasure they're looking for is hidden.
* TheLeader: Jupiter Jones is a Type I example, since he most certainly is a mastermind, assembled his friends for the specific purpose of becoming investigators, is always the one with goals for a case and coming up with the boys' plans, is even more of TheSmartGuy than Bob, and is often a GuileHero. He's also a Type IV, being the most charismatic of the three and the one who (other than a few examples of grumbling and mutiny, usually from the CowardlyLion Pete) is always listened to and agreed with. He appoints himself First Investigator and makes no effort to hide why he considered this the right choice, demonstrating time and again what skills place him in the position. At the same time, despite his pomposity, he always gives Bob and Pete credit where it is due, working to include their thoughts and reasoning in cases, never belittling them or their skills (at worst getting annoyed when they don't see an "obvious" clue that he does, or gently mocking Pete for his cowardly ways). He makes an effort on several occasions to point out to clients how all three of them are essential and have important roles, times when only they can do what needs to be done, and he also encourages them to be more proactive in pursuing clues and thinking deductively even as he remains in charge.
* LemonyNarrator: In ''Whispering Mummy'', after Hamid is horrified at Americans eating dogs: "But there was no time now to explain about the mysteries of the American hot dog."
* LinkedListClueMethodology: Twice. The first time is played with--in ''Stuttering Parrot'' the messages of the seven birds all lead generally to one place where the treasure is hidden, but each message after the ones which lead them there are part of a linked chain to help them find the exact hiding place. Played straight with the "Dead Man's Riddle", although if Jupiter had recognized a stealth clue in the reference to a "posh Queen" he could have taken a shortcut and jumped straight to the end of the riddle.
* LiteralMinded: During the Crimebusters series, Pete once gave Jupiter a hard time because during one chance he had with a girl, he ended up blowing it by boring her with a detailed explanation of the structure of the atom because "she wanted to get to the basics." It didn't cross his mind what she really meant until he tried to defend his actions and everyone began laughing.
* LiteraryAgentHypothesis: Intriguingly, the very first book has Jupiter offer this to Alfred Hitchcock as a [[LeaningOnTheFourthWall meta-justification]] for why the director was used to 'introduce' the series--he claims that all successful, well-known detectives had someone who wrote their cases for them, thus making them known to a larger audience and lending their notoriety to the marketing process. (As stated above, it can't be denied that tying the Three Investigators to someone famous helped boost sales of the books.) For the boys, Jupiter claimed that while he wanted Hitchcock to introduce their cases, the actual texts would be InUniverse {{Fictional Document}}s written by Bob's reporter father from his son's notes--implied to be the very books the reader was reading, of course. (After seeing the more harrowing details of some of their cases, it's amazing Mr. Andrews even allowed the firm to continue!) Most amusingly of all, Jupiter claims Sherlock Holmes ([[UrExample of course]]), Hercule Poirot, and Ellery Queen were other detectives who had been made famous by those who wrote their books, [[ATrueStoryInMyUniverse implying they were all real people with real cases]]. But it makes sense that they'd be real to Jupiter, since [[MutuallyFictional he's a fictional character too]].
* LockedRoomMystery: A near-literal example occurs as a subplot in ''Shrinking House'', where the boys have to figure out how someone has been getting in and out of an impregnable concrete art studio with only one locked door in order to move Joshua Cameron's paintings. [[spoiler:Turns out there ''is'' another entrance that was overlooked--a hole high in the back wall holding an exhaust fan.]]
* LongRunningBookSeries
* LookBehindYou: [[spoiler:Roger Callow]] of ''Dead Man's Riddle'' actually falls for the subverted version of this trope--being sure that the boys were simply trying to make him turn around so they could get away, when in actuality Billy really was behind him and could run off to warn the police.
* LoopholeAbuse: In ''Smashing Glass'', when the boys need to see the police reports on their stakeouts to try and figure out who the smasher is, Chief Reynolds informs them that unfortunately such things are classified, with only a court order allowing it...but that thanks to freedom of the press, reporters can ask to see them. Cue Bob going to his father and having them all hired as stringers for the day, complete with press badges, so they can do just that. [[note]]Either Bob's father has a huge amount of clout at the paper to do this without consulting with his boss first (perhaps because he's their star reporter?), or everyone at the paper knows (thanks to him) about the Three Investigators, and so hearing they are on the case, they want to assist in solving such high profile vandalism.[[/note]]
* MacGuffin: While usually the boys are pursuing [[PlotDevice important clues/items]], or even the actual treasure, just as often it's an item with little or no purpose (the Silver Spider of Varania is needed to crown its king and thus needed to prevent the RegentForLife plot of the EvilChancellor, but otherwise does nothing), it's only a clue or a hiding place for one that leads somewhere else (the crooked cat, the haunted mirror, the paintings from ''Shrinking House'') and thus becomes irrelevant once it has served its purpose, or it's a RedHerring. Appropriate that this would appear, [[Creator/AlfredHitchcock considering who the series is named after]].
* MacGuffinDeliveryService: In most of the stories with riddles leading to lost treasures, the villains sit back and wait for the boys to solve it for them, then swoop in to take it from them. Sometimes the villains are figuring out the riddle too and thus [[OneTrueSequence happen to arrive at a location]] [[MacGuffinMelee at the same time as the boys]] (justified in LinkedListClueMethodology cases--because the clues have to be figured out and followed in order, the heroes and villains meeting up is bound to happen eventually) and ''then'' take it away from them, but usually they merely follow the boys and let them do the work. Classic example: the Percivals from ''Dead Man's Riddle''.
* MacGuffinMelee: ''Dead Man's Riddle'' is a particularly striking example, with the Investigators, the Percivals, Skinny Norris, ''and'' [[spoiler:Roger Callow]] all looking for the treasure, although it never gets passed between them. In ''Dancing Devil'' it turns into the actual exchange version of the trope, where the statue passes from the neighborhood bully, to a local homeless man, to a seedy antiques store owner, and finally to an unscrupulous art dealer before the Investigators catch up with it.
* MadScientist: Played with in ''Wandering Cave Man''--one of the Spicer Foundation's resident scientists is literally this (in the sense he has a HairTriggerTemper) but is otherwise nothing like the trope, while the villain of the story has none of the trope's usual hallmarks but ''is'' willing to commit crimes and unethically discredit his colleagues in a desperate attempt to get the needed funding for his research.
* MagneticPlotDevice: Also happens a lot, usually with whatever item they're seeking or the clue which will solve the mystery/find the treasure, but the crooked cat and the paintings from ''Shrinking House'' take the cake.
* MakeItLookLikeAnAccident: The creators of the ScamReligion in ''Singing Serpent'' at first use this method when eliminating the enemies/rivals/targets of petty jealousy that the cult members wish done away with--specifically, making the woman whom Allie's aunt wanted out of the way (so she could acquire a coveted item from a celebrity auction) have a car accident thanks to tampered brakes. Previous victims may or may not have been dealt with similarly, but by the time the Investigators learn they must warn a deli owner's rival of an incipient bomb, it's clear the con men don't particularly care about disguising the nature of what they're doing.
* ManipulativeBastard: [[spoiler:Mr. Harris]] of ''Laughing Shadow''. Not only is he a ConMan who is using and misleading Miss Sandow in order to get the Chumash Hoard (and is using child slave labor to find it), he manages to fool Jupiter into thinking he's a good guy and encourages his false assumptions about Ted Sandow being the villain so that he can kidnap Bob and Pete, then nab the treasure. He would have gotten away with it if it hadn't been for his pet kookaburra and the telltale evidence proving [[spoiler:he wasn't actually a vegetarian]].
* MasterOfDisguise: Stephen Terrill, [[FamedInStory the Man with a Million Faces]]. [[ChekhovsGun This is plot-significant]] when it seems [[spoiler:Terror Castle is being "haunted" by a whole slew of elaborately dressed, stereotypical figures, supposedly an international gang of smugglers using the place as a hideout]].
** Also, Laslo Schmidt of ''Moaning Cave'' and [[spoiler:the Amazing Gabbo]] of ''Crooked Cat''.
* MaybeMagicMaybeMundane: It is never explained how the old [[UsefulNotes/{{Romani}} gypsy king]], Anton, has the knowledge he does in ''Silver Spider''--after using an herb of some sort as a truth serum and being unable to learn where the missing spider is thanks to Bob's lost memory, he makes two odd pronouncements to [[EvilChancellor Duke Stefan]]--that he heard a bell ringing for victory, and that the spider was in the end "only a spider". The former could conceivably be a good guess on his part thanks to knowing the story of the bell of Prince Paul like every other Varanian--like the Delphic oracle to Darius, he could claim a bell would ring for victory [[PropheticFallacy no matter who actually won]]. [[PropheciesAreAlwaysRight But how did he know that]] [[spoiler:the spider was hidden near a real spider web, thus making it "only a spider"]]?
* MeaningfulName:
** [[PosthumousCharacter Diego Manolos]], ConMan and blackmailer, turned out to be TheManBehindTheMan when it came to manipulating and controlling Ruffino, and his hand could be said to be indirectly behind everything that happened in ''Haunted Mirror''. Manolos, meanwhile, is rather reminiscent of the Spanish word for hand, "manos". It is also only one letter away from "Manolo", a common nickname for Manuel which means "God is with Us" (and Diego Manolos certainly acted like a god, playing with people's lives and doing everything he could to gain as much power and riches as he could).
** Roger Callow of ''Dead Man's Riddle''--he is described as young and somewhat inexperienced as a lawyer, which matches his last name perfectly.
** August August of ''Fiery Eye''.
** Bert Clock, professional screamer who liked to collect clocks, and eventually had them all modified so as to scream in place of an alarm--and his nickname was also Screaming Clock.
** Professor Shay of ''Phantom Lake'' [[spoiler:turns out to be a bit shady]].
** Jupiter Jones [[StealthPun himself]]--named for the [[IAmBigBoned largest and most massive planet]] in the solar system, as well as the [[TheLeader king of the Roman gods]].
** Maybe unintended - but doesn't Victor say a [[IncrediblyLamePun huge nay]] to society?
** Walter Quail of ''Dancing Devil'', who is extremely timid, twitchy, and nervous most of the time.
** The Burroughs couple of ''Sinister Scarecrow'' [[spoiler:burrow underground to rob the Mosby Museum]] while Gerhart Malz [[spoiler:("mal" meaning bad) turns out to be a forger]].
** Charles Barron of ''Blazing Cliffs'', and his illegal practices with the government, labor disputes, discrimination, and environmental regulations which essentially made him a robber-baron industrialist of the last-century. Invoked in-story by his enemies and victims who called him the Robber Barron, and lampshaded by Jupiter.
** Maureen Melody of ''Two-Toed Pigeon'', who owns many singing birds and sings constantly herself.
** Jeremy Pilcher of ''Cranky Collector'', whose last name is an obsolete word meaning "a contemptible person"--and is one letter away from "filcher", an apt description as well considering his secret thievery of emeralds from the lost mine to bolster his finances.
* MechanicalMonster / {{Robeast}}: The eponymous [[spoiler:''Coughing Dragon'']] turns out to be one of these, [[spoiler:a prop from an old movie set]].
* TheMeddlingKidsAreUseless: Unlike ''TheHardyBoys'' and ''NancyDrew'', completely averted. The boys are always instrumental to finding the treasure/heirloom/lost loot in question, with the cops instead showing up to be the muscle to arrest the villains and, often, providing information to the boys so they can solve the case. The few times where the cops and other adults are more proactive, the boys are still the ones to solve the riddle, provide the proof of the villain's scheme/identity, or explain the nature of the story's events.
* MicroMonarchy: Varania of ''Silver Spider''. Based on the descriptions (and illustrations) of the place, it seems mostly modeled off of Luxembourg or Liechtenstein, although the nature of the Minstrel Party, some of the naming conventions, and the presence of Roma bring to mind ''The Trumpeter of Krakow'' and therefore Eastern Europe. The Republic of Lapathia from ''Flaming Footprints'' used to be one before its revolution, and although afterward it no longer has a king it otherwise still conforms to the trope. Ruffino of ''Haunted Mirror'' is another republic variation.
* MightyWhiteyAndMellowYellow: This seems to have been the nature of the relationship between Matthias Green and his Chinese wife in {{Backstory}}. Rumors suggest Green had trouble with nobles in China, which could have been either because of his theft of the Ghost Pearls or his theft of the Chinese princess he wed. The publication date of the book suggests Arthur would have been well aware of the stereotypes regarding white men and Asian women, either from Vietnam or Korea, or UsefulNotes/WorldWarII before it. On the other hand, however the relationship started, it seems clear there was genuine love involved--Mr. Won, when speaking of the matter, observed that Green had "stolen" a bride but also that "women follow their hearts", and the way Green made a memorial coffin for her in a secret room suggests great devotion. And while he took to wearing Mandarin robes in his mansion, something that could suggest a fetishizing of the exotic Eastern Other, it's just as likely (when combined with them having only Chinese servants) that he was doing it to make her feel at home or because he had even come to genuinely enjoy the culture himself. So if this was how the two became involved, it at least seems to have been a bit more complicated and realistic than the stereotype.
* MinorCrimeRevealsMajorPlot: Classic example in ''Missing Mermaid'', where the disappearance of Todd Stratten ends up uncovering not only [[spoiler:Clark Burton]]'s secret other life as a fence and thief but also his involvement with Mooch Henderson's roommate and the slave market (which in turn inadvertently reveals Mooch's racket with stealing dogs and then 'returning' them for rewards). As if that isn't enough, the manner in which the whole thing is revealed is ''also'' an example, since in order to keep anyone from knowing about his connection to Todd's vanishing and Tiny's death, or that Todd had discovered his secret room and stash of money, he threw the broken mermaid statue (which got damaged during the discovery of his crime and led to the dog's death) off the pier...[[RevealingCoverUp but doing this instead of just tossing it in the trash is what drew the boys' attention to him in the first place]].
* MirrorScare: Unsurprisingly this happens with the "ghost" seen in the eponymous ''Haunted Mirror'', complete with quite an example of a NightmareFace (and accomplished by means of a well-hidden BookcasePassage, of course).
* MoustacheDePlume: Author Mary V. Carey wrote under the name M.V. Carey, presumably because Random House thought the boy readers of the series wouldn't read books written by a woman.
* MultilayerFacade: The villain of ''Crooked Cat'', [[spoiler:the Amazing Gabbo]], uses one of these--wearing [[spoiler:his clown costume]] over his regular old man appearance [[spoiler:which is in turn a disguise hiding his true youthful self that he ''takes off'' to commit the BankRobbery, but with the ''addition'' of a tattoo]]. It's also a form of LivingADoubleLife, since he's hiding [[spoiler:his true self so as to appear as a harmless old man]].
* MummiesAtTheDinnerTable: Borderline example--while as far as we know Mr. Green of the Green Mansion never did this with his wife's corpse, he did stash her body in a secret room in his house, laid out in a coffin with her finest clothes and the [[MineralMacGuffin Ghost Pearls]].
* MysteryFiction
* {{Mystery Magnet}}s: A corollary to being a KidDetective.
* NaturalSpotlight: At the climax of ''Headless Horse'', after days of rain and flooding, [[CueTheSun the sun finally comes out]] right when Jupiter solves the mystery--by having a sunbeam shine down right on the jewel-encrusted Sword of Cortes.
* NeedleInAStackOfNeedles:
** In ''Whispering Mummy'' after having escaped the warehouse where the villains were keeping the mummy and its case, Pete marked it with a question mark so they could find it again. Thanks to being chased from the area before they could learn precisely where they were, the Investigators were forced to use a Ghost-to-Ghost Hookup to locate the mark. However, one of the friends of friends who had been called happened to tell JerkJock [[ArchEnemy Skinny Norris]] about it, and so he and his gang proceeded to mark numerous buildings in that area of town to make them lose the trail (and even called, pretending to be an informant, in order to get them to come to a particular building so he could gloat at them).
** In ''Nervous Lion'' the [[spoiler:cage bars]] which contain the smuggled diamonds were at one point hidden in the junkyard next door to Jungle Land...leading to the unenviable task of looking among nothing but steel parts and pieces for other things made of steel.
** In ''Dead Man's Riddle'', the boys figure out the fortune is hidden by a bed on the ''Queen of the South''...but the ship has over 500 of them, necessitating them finding a way to narrow it down.
* {{Nephewism}}: Jupiter Jones lives with his aunt and uncle, his parents having died in an accident when he was very young. By contrast both Bob and Pete's parents are shown on numerous occasions, and sometimes even have significant roles in the stories.
* [[NeverOneMurder Never One Crime]]: The villain in ''Invisible Dog'' commits quite the slew of crimes. Not only does he steal the Carpathian Hound and then extort money from its owner for its safe return, but he knocks out and nearly kills the church caretaker while hiding there, and after hiding the hound [[spoiler:in the pool]] he poisons one tenant [[spoiler:who takes midnight swims]], plants a bomb under the hood of the manager's car [[spoiler:because she was planning to have the pool drained and cleaned]], and starts a fire in another tenant's apartment [[spoiler:to give himself an alibi for the ransom exchange, being safely in a nearby hospital after feigning being overcome by the smoke]]. All of this, of course, was done so he could obtain the money [[spoiler:to replace that which he'd taken from his nephew's trust fund and lost in stock market speculation]].
* NeverSayDie: Although the boys never really come too close to death, the danger they suffer is often very real and both they and their families worry about getting injured or killed. Of course the worst violence they usually suffer is getting knocked out and/or BoundAndGagged / LockedInAFreezer. But in ''Dead Man's Riddle'' they do almost [[InevitableWaterfall go over a waterfall]], and in the early book ''Green Ghost'', when Jensen asks Mr. Won what to do if the boys don't turn over the Ghost Pearls, [[WhamLine he coldly tells him to slit their throats]]. The threats Three-Dots makes with his SwordCane in ''Fiery Eye'' (and his supposed YouHaveFailedMe killing of one of the Black Moustache gang) are taken quite seriously as well. They are also held at gunpoint several times (''Stuttering Parrot'', ''Vanishing Treasure'', ''Screaming Clock'', ''Laughing Shadow'', ''Flaming Footprints'', ''Singing Serpent'', ''Shrinking House'') and are left to die in the desert in ''Death Trap Mine''. Pete did drown in a pool once, though Frank brought him back.
* NobodyHereButUsStatues: The burglar in ''Invisible Dog'' actually pulls off this one, disguising himself as a statue of St. Patrick in the neighborhood church using a pageant costume.
* NoHonorAmongThieves: In several cases the villains turn on each other, allowing the boys to escape and/or capture them (''Skeleton Island'', ''Screaming Clock'', ''Shrinking House''). ''Scar-Faced Beggar'' is notable for the fact it's actually one of the villains lacking honor [[EvenEvilHasStandards while the others retain it]] which causes the falling-out (they believe in what they consider a patriotic cause, he's just in it for the money and is secretly robbing them on the side).
* NonindicativeName: Most of the books' titles (save some of the more modern entries in the series) had names which related directly to the plot, albeit sometimes in a subtle or more mysterious way, but at least one has generated some confusion due to its vagueness: ''The Mystery of the Vanishing Treasure''. The book does involve a BankRobbery and the theft of a priceless belt from a museum, but none of this is clear from the title alone.
* NotAllowedToGrowUp: This is particularly noteworthy because it was attempting to age the boys up in one of the modern relaunches of the series that ultimately killed it in the United States.
** This is subverted in the German releases of the series however, with the boys aging extremely slowly. In their over 30 years long history in Germany the boys have aged only about five to six years. This is in part due to the fact that the ''Crimebusters'' spinoff was regarded as a straight continuation of the original series and partly because the popularity of the Audio Adaptations' voice actors didn't allow for them to be switched out without losing the majority of their audience. Though all three actors have hit 50 by now, they can still convincingly portray 18-19 year olds but sound distinctively too old for 13 year olds.
* NothingIsScarier: A great deal of this appears in ''Phantom Lake'', surprisingly--the empty, ominous GhostTown of Powder Gulch; Mrs. Gunn, sitting alone in the lodge, listening to the sound of someone smashing stone in the night, until they all trek through the woods to find the collapsed smokehouse; the descent into the empty, shadowy quarry lit only by small bits of moonlight; and especially the visit to the fog-enshrouded Cabrillo Island, covered by the eerie twisted cypresses, knowing someone might be out there hidden in the mist...
* NotInFrontOfTheParrot: Inverted in ''Stuttering Parrot''. Parrots taught clues to the location of a hidden treasure have been so badly traumatized by their treatment at the hands of criminals that they refuse to talk. Fortunately, a mynah bird in the group (a last-minute replacement for a dead parrot) has memorized all the clues, and can be easily coaxed to repeat them.
* NotMeThisTime: Hugenay, in ''Screaming Clock''.
[[/folder]]

[[folder: Tropes O-S]]
* ObfuscatingDisability: [[spoiler:Mrs. Chumley in ''Sinister Scarecrow''.]]
* ObfuscatingInsanity: Old Ben the prospector from ''Moaning Cave'' uses this to misdirect people away from the mine where he and his partner are digging for stolen diamonds.
* ObfuscatingStupidity: Jupiter Jones, in many a case. He's the smartest person in the group, but because he is a former child actor and a little plump, he can act unintelligent in order to disarm people and get information from them that he wouldn't get otherwise. Every once in a while though a canny villain sees through the act.
* OminousPipeOrgan: Terror Castle has one that supposedly is played by the Blue Phantom. Justified by Stephen Terrill having been an actor who not only liked to play his films for guests but came from the silent era when pipe organs were actually used in theaters to provide incidental music. It also contains pipes which [[ShownTheirWork play notes so low as to be subsonic and affect the human nervous system]], thus instilling instinctive terror.
* OnceAnEpisode: The boys will show their business card, with the slogan "We Investigate Anything", to someone, usually a prospective client. After ''Green Ghost'', when their assistance proved invaluable to Chief Reynolds, they were given a card from him as well identifying them as junior deputies--something which was sometimes needed to convince clients that three boys could be real detectives, let alone useful ones. Also once an episode, there would be an introduction from Alfred Hitchcock (actually written by the author, and later replaced by Hector Sebastian) with a few teaser details about the case at hand and the rest being a nearly identical explanation of their background and how they got together. And there would always be a meeting with their mentor at the end, explaining details which couldn't be covered in the main narrative and otherwise wrapping the case up.
* OneSteveLimit: Averted once, where the villain's right-hand man in ''Green Ghost'' and one of Anna's inn guests in ''Monster Mountain'' both have the name Jensen. The latter seems suspicious at first since he is faking being a nature photographer, but it turns out he is just there to protect Anna from her ConMan husband, who had also swindled his sister. Also, the villains of both ''Coughing Dragon'' and ''Scar-Faced Beggar'' share the name Shelby (albeit as a last name and first name, respectively) although they could not be more different since one is a repentant and mostly harmless trickster while the other is an arrogant, entitled thief, rebel, and traitor.
* OrwellianRetcon: After 1980, the conceit of having Creator/AlfredHitchcock introduce (through ghost writers) the books and interact with the boys was [[AuthorExistenceFailure no longer feasible]]. As a replacement, the authors created a mystery writer named "Hector Sebastian." Some editions of the earlier books written with Hitchcock as a character replace him with Sebastian (or the fictional director Reginald Clarke).
** The German version had held the rights to the Creator/AlfredHitchcock name well into the 00s [[RuleOfCool and just kept on using it]] until replacing it with the SuspiciouslySimilarSubstitute [[CaptainErsatz Albert Hitfield]] when the rights finally expired.
* OutOfCharacterMoment:
** Although Pete and Bob have always had a certain humorous tendency to make jokes at Jupe's expense (either regarding his intelligence or his weight), the moment in ''Missing Mermaid'' where they both mock him for getting stuck in the dumbwaiter chute and even take his picture for the firm scrapbook is surprisingly and unusually mean-spirited of them--and it gets even worse when they mock him again while showing the developed picture to Hector Sebastian at the end of the book. Sebastian is quite right to reprimand them with the warning they might become "the Two Investigators" if they weren't careful.
** In order to lure out the villain in ''Smashing Glass'', the boys decide they need bait. Jupiter wants to use the Rolls Royce. Despite showing trepidation, uncertainty, and wincing greatly at the possibility, Worthington allows it as a necessary duty undertaken in order to solve a case. While it's true that Worthington's protectiveness of the car could have eased over time, especially after having become an unofficial "fourth investigator", it still seems incredibly unlike the man who once refused to abandon the vehicle until he absolutely had to (to save Jupe and Pete inside Terror Castle) to allow something like this--and even if he himself had become more sanguine to the possibility, surely he would get in great trouble with the rental agency if he allowed damage to happen to the Rolls while it was under his care. To be fair to Arden, however, he rarely used Worthington much in his entries in the series, so it may be he had forgotten the character's foibles when the time came to write this scene. (On the other hand, plot-wise the situation could have been handled just as easily with Hans or Konrad using one of the salvage yard trucks as bait.)
* PhotographicMemory: Jupiter.
* PoliticallyIncorrectVillain:
** Skinny Norris, in ''Headless Horse.'' While prior to this his arrogance, nastiness, and superiority would make such an attitude unsurprising (especially for a SpoiledBrat like him, and ''especially'' in California where matters of immigration and ethnic foreigners have always been [[RuleOfCautiousEditingJudgment rather contentious]]), his attitude toward Diego and Pico and his use of an outdated slur [[note]]wetback[[/note]] directed at them does come a little out-of-nowhere, and the fact this appears in the book where he commits his worst villainy and is subsequently PutOnABus for the rest of the series is probably not an accident. May be justified by the influence of ranch manager Cody who, based on his manner of dress and his three saddle-tramp robber friends, is most likely from Texas and thus could have brought such attitudes (and that specific slur) with him.
** The extremist kidnappers of ''Deadly Double'' are also this, with the two who have Jupiter and Ian going on about the native "savages" while [[spoiler:Anna Lessing]] proudly proclaims her "patriotic" loyalty to a safe and free Nanda, belonging only to the whites who "own it and will keep it", and calls the native Nandans "a mob of uncivilized blacks." Completely justified by the place and time they hailed from, being an {{Expy}} of South Africa under apartheid.
* PortraitPaintingPeephole: There's actually one of these in Terror Castle. Justified by both the nature of the plot (human agency being behind the haunting) and characterization (the castle's owner was a silent horror film star who built his home to be modeled off of his movies).
* PowerTrio: Arguably the BeautyBrainsAndBrawn variation, with Jupiter as TheSmartGuy, Peter as TheBigGuy and Bob as the most sociable one. Though the Freudian model (Jupiter - Superego, Pete - Ego, Bob - Id) might cast an interesting light on [[AlternateCharacterInterpretation tentative hidden sides of]] [[CovertPervert Bob Andrews]] (he ''does'' become a ChickMagnet in the modern relaunch of the series)...
** At least in the German audio adaptation Bob seems to alternate between TheCasanova and HandsomeLech with quite a bit of ChickMagnet thrown in. He even seems genuinely offended when a female client of theirs mistakes his [[LameExcuse bumbling effort at a distraction]] for [[CannotSpitItOut a bumbling declaration of love]] and [[HilarityEnsues actually turns him down.]] So there might be something to that AlternateCharacterInterpretation...
** Also Peter has turned into a more traditional example of [[DumbMuscle the brawn]] being exeptionally gifted at [[NewPowersAsThePlotDemands whatever sport the plot requires him to]] while also being a [[TheDitz somewhat naive]] CowardlyLion due to a mix of {{Flanderization}} and CharacterizationMarchesOn. While this makes him very close to a BrainlessBeauty or DumbJock, he's saved by the fact that he's interestingly also the group's resident DeadpanSnarker.
* ProperlyParanoid: In ''Trail of Terror'', Pete's grandfather is convinced from practically the start of the book that his neighbor Mr. Snabel is spying on him and deliberately causing trouble for him, and after the group unexpectedly encounters him on a beach and then in a nearby town, he becomes further convinced the man is following him and trying to steal his invention. The boys dismiss him at first, but after Snabel keeps turning up again and again, and in ways that make it impossible to be a coincidence (not to mention inexplicable, since they know they didn't see him following on the highway), it becomes harder to deny. Once Snabel is seen with a gun, the suspicion is proven justified, and especially once a tracking device is found on the car--but it turns out it had nothing to do with the invention, instead it's a spy case they stumbled into when accidentally taking some of the evidence.
* PsychicDreamsForEveryone: Or at least for old Mrs. Denicola in ''Scar-Faced Beggar''. Interestingly, while many of her dreams foretell danger, others do not (such as predicting the arrival of her future daughter-in-law in her life).
* PutOnABus: Despite [[HeelFaceTurn seeming to reform]] after being used and abandoned by [[spoiler:Marechal]] in ''Shrinking House'', Skinny Norris almost gets the boys killed in ''Dead Man's Riddle'' and appears at his nastiest and the closest he comes to true criminal activity in ''Headless Horse'' (aiding and abetting Cody in concealing who started the brush fire and framing Pico for it). When the truth comes out he is sent away by his father to military school and never seen again in the series. Said by WordOfGod to have happened because Skinny's character was too flat, limited, and uninteresting to be useful to the series.
** The German version [[TheBusCameBack brought him back in a cameo appearance]] in book 85 ''The Tower of Fire'' until he later made a full return in the anniversary/three-parter episode book 100 ''The Island of Death''. He has been [[CommutingOnABus a recurring character ever since.]] He even got his own [[ADayInTheLimelight day in the limelight]] of sorts when Bob suffered from TapOnTheHead induced IdentityAmnesia and Skinny [[PetTheDog wound up taking care of him]]. While Skinny still causes his usual amount of havoc, he also seems genuinely fond of Bob and helps him out even after he regains his memories, setting himself up for more of a JerkWithAHeartOfGold role. Although it [[DependingOnTheWriter depends on the writer.]]
* RealAfterAll: Aside from the fact the monster of ''Monster Mountain'' turns out to be a genuine [[BigfootSasquatchAndYeti mountain man]], several of the entries involving the supernatural written after M. V. Carey took over the series turned out to be real, or at least implied to be. In a chillingly effective moment at the end of ''Haunted Mirror'', the villain sees ''something'' in the supposedly cursed glass that makes him flee right into the arms of the police; unable to explain it, the boys look very uneasily at the mirror and quickly leave. More obviously, when one of the villains of ''Magic Circle'' flees the scene only to crash in Beefy's car while the witch of the eponymous circle looks on with grim vindication, the boys have to wonder if she cursed him for what he had done to her; Jupiter scoffs at such notions of course, and a true Wiccan would not curse lest she run afoul of the Three-fold Rule, but... In ''Invisible Dog'', not only does Sonny Elmquist turn out to be a real astral wanderer, but it seems quite likely that the phantom priest seen in the church was a real ghost. In ''Scar-Faced Beggar'' old Mrs. Denicola has genuinely psychic dreams. And the ghost which haunts the attic of Mr. Pilcher's "cursed" house in ''Cranky Collector'' is apparently this as well, considering both Pete and a police officer hear its footsteps and feel the cold of its passage, but see nothing (and it leaves no footprints in the talcum powder Pete put on the floor).
* ReclusiveArtist: [[invoked]] Madeline Bainbridge of ''Magic Circle''. Discovered young by a talent agent wowed by her beauty and instantly given a lucrative contract, her career reads like an {{Expy}} of Elizabeth Taylor--constantly in the public eye, famous and beloved across the country, star of numerous sweeping, big-budget, period epics, known for a coterie of fellow actors and other Hollywood notables, and involved in a public scandal due to romance on the set between herself and her male co-star. She never quite became a WhiteDwarfStarlet, but her [[TroubledProduction final film]] was [[BoxOfficeBomb widely derided as a ridiculous, overblown flop]], and while it was Ramon Desparto's death which caused her to go into seclusion, it's possible her career might never have recovered from it. In any event, she cut herself off completely from the world, refusing all visitors, never watching television and rarely using the telephone, and allowing all of her business affairs to be handled by her manager/former chauffeur. [[spoiler:[[ConMan This turned out to be a mistake]].]]
* TheRedBaron: The Whisperer, aka Jonathan Rex from ''Terror Castle''. Also, El Diablo of ''Moaning Cave''.
* RedHerring: Happens a lot--rarely ever is the boys' initial suspect the true criminal, nor is the thing they seek found in the first place they look. A particularly good one was in ''Death Trap Mine'': the fact Mrs. Macomber had suddenly left her job, disappeared for several months, came into money out of nowhere when she had been destitute and forced to work at what had once been her own store, matched the description of a member of a holdup gang, and then vanished after a newspaper referencing the robbery was discovered all led Jupiter to believe she was a member of the gang and possibly the one who killed the man found in the mine. But instead [[spoiler:she'd come into money when a relative died, and been kidnapped by Thurgood for recognizing he was an imposter]], and the rest was all coincidence.
** Another good example: Rory from ''Phantom Lake'' whose whole purpose in the plot, other than being a ViolentGlaswegian, was to distract the reader from wondering who might really be Java Jim or his accomplice. On the one hand, his constant attempts to convince the boys to stop looking for the treasure, his conveniently timed comings and goings, and his various misdeeds all made a great candidate for the villain--too obvious, in fact. Which might cause some readers to get suckered into thinking he was guilty, while others would dismiss him but then be left not knowing who the real villain was. [[spoiler:Anyway, he wasn't Java Jim--he just didn't want Mrs. Gunn to be rich because he was afraid she wouldn't accept his marriage proposal. A bit of UnfortunateImplications there--what she wants doesn't matter? She can only be rich if he earns it for her and takes care of her?--but otherwise a CrowningMomentOfHeartwarming and [[CrowningMomentOfFunny Funny]] in one.]]
** Not only are there a large number of characters in ''Shark Reef'' who could possibly be the villains (since all their motives in being involved in the oil rig protest plot are rather opaque), but in several successive chapters Arden does a stupendous job of making Captain Jason, [=MacGruder=], Yamura, and the Connors brothers all look very suspicious, the latter three by having all of them follow each other around. The Connors (the actual main antagonists) even tell a story designed to make [=MacGruder=] look suspicious as an invoked example of the trope.
** For a time the boys are fooled in ''Purple Pirate'' into thinking that what the villains are looking for is lost BuriedTreasure belonging to the eponymous pirate. Helped along by [[spoiler:Joshua Evans]] claiming he was looking for just such a thing as his rightful inheritance, and purchasing a trunk that he branded with the pirate's name to hold the gang's robbery loot. Too bad for him the chest, its fastenings, and the branding were all too new and modern to have held PirateBooty.
* RegentForLife: A desire to make this happen kicks off the plot of ''Silver Spider''.
* RevealingSkill: The fake El Diablo gives himself away in this manner in ''Moaning Cave''--by appearing as [[ASinisterClue left-handed]]. [[spoiler:[[SubvertedTrope Not because the villain himself was left-handed]], but because the boys had discovered from finding El Diablo's skeleton that he was right-handed. The only one who would portray him left-handed was the one whose [[ItsAllAboutMe pet theory]] said so--Professor Walsh.]]
* RevisitingTheRoots: After Arthur's death, most of the subsequent books in the series revolved around searches for bank robbery loot, lost heirlooms, con men, smugglers, and various other crimes. However, Arthur's fondness for mysteries involving Hollywood and the acting community (thanks to his background) returns in four later books: ''Magic Circle'', ''Missing Mermaid'', ''Rogues' Reunion'', and ''Creep-Show Crooks''. There's also a welcome return of the sort of banter and humor Arthur was known for in some of the later books.
* TheRevolutionWillNotBeVilified: Both the history books and General Kaluk insist in ''Flaming Footprints'' that the revolution which ended the Azimov line in Lapathia was peaceful and relatively bloodless, carried out by the will of the people (or at least, to protect them), and that the royal family either ended their own lives or fell prey to various terrible accidents. But considering WrittenByTheWinners, the Potter's fury and resentment toward Kaluk, the latter seeming very much like a GeneralRipper fond of ColdBloodedTorture, and [[NothingIsScarier whatever was in the picture he showed the Potter of the last Azimov]], it seems far more likely to have been [[TheRevolutionWillNotBeCivilized uncivilized]]--which rather well parallels how the Azimov family came to power in the first place, as lampshaded by Kaluk himself.
* SatchelSwitcheroo:
** The plot of ''Two-Toed Pigeon'' basically revolves around everyone performing this trick multiple times using living creatures (the pigeons): Blinky's entire scheme involves replacing Frisbee's pigeons with his own so he can collect the pearls instead; after accidentally forgetting his pigeon with the boys, he comes to steal it back and replaces it with one of Frisbee's; and in the end the boys succeed in flushing him out by replacing one of his pigeons with the one they had, so that Blinky would receive a pigeon with their business card while they received a pearl. This is all made possible by the pigeons all being the same breed and color, with the only identifying feature to tell them apart being the eponymous number of toes.
** An even more textbook example occurs in ''Trail of Terror'' when Bob and Mr. Snabel accidentally switch cameras (it's even helpfully noted in the text that they're the same brand, and they're set down next to each other on a bench). PlayedForDrama, however, rather than comedy because Snabel's camera contains evidence of military engineering secrets which he is selling to a foreign spy, causing both of them to pursue the boys and Pete's grandfather across the country and resort to arson, kidnapping, and more to get it back.
* [[SavingTheOrphanage Saving the...]]
** Film Production: ''Skeleton Island'', where the haunting is threatening Pete's dad's film shoot.
** MicroMonarchy: ''Silver Spider'', where the eponymous badge of office must be found so the prince can be crowned and prevent the EvilUncle / [[EvilChancellor Chancellor]] from becoming RegentForLife and turning the place into a WretchedHive of criminals.
** Circus: ''Crooked Cat''
** Jungle Theme Park: ''Nervous Lion''
** Ranch: ''Headless Horse'', complete with the evil developer being none other than [[ArchEnemy Skinny Norris]]'s {{Jerkass}} father (though he does at least confine himself to legal means, for the most part) and with the solution being finding a long-lost family heirloom. Proof that this trope really can work for any plot.
* ScaryScarecrows: The eponymous ''Sinister Scarecrow'', complete with SinisterScythe at one point.
* ScoobyDooHoax: The frequent explanation behind seemingly supernatural happenings. Textbook examples include ''Terror Castle'', ''Green Ghost'', ''Skeleton Island'', ''Flaming Footprints'', ''Haunted Mirror'' ([[RealAfterAll maybe]]), ''Dancing Devil'', ''Sinister Scarecrow'', ''Wreckers' Rock'' (although only as a subplot), and ''Blazing Cliffs''. The latter is an extremely over-the-top and overly complicated example, but justified by the villains in question being rather desperate and including failed actors among their number, and that they are playing to a paranoid and credulous audience.
* ScreamingWoman: Letitia Radford of ''Sinister Scarecrow'', although she has pretty good reason for being so, and by the end of the book she has recovered and proven she's made of sterner stuff after all.
* SecretPassage: Terror Castle has two of them--one behind a mirror that leads to the projection room with its OminousPipeOrgan and Blue Phantom, the other underground connecting the dungeons to [[spoiler:Jonathan Rex's parakeet enclosure]]. A few other books have secret passages too, or at least secret rooms.
* SeparatedByACommonLanguage: To a certain degree this happens with Dingo Towne's riddle in ''Dead Man's Riddle'' due to it being written in [[UsefulNotes/BritishEnglish Cockney rhyming slang]]--also see the confusion generated by "billabong", and the stealth clue in "posh Queen". But it undeniably appears in a key moment to completely undo the villain's scheme in ''Dancing Devil'': the artist he hires to create a reproduction of the eponymous statue has only a small photo to work from, so for the finer details he depends on a written description. However the book which provides it was published in England, and so it uses the word "corn" to mean a sheaf of wheat while the artist, being American, assumes it means what the British call maize (corn on the cob, of course) and thus puts the wrong item on the statue's belt.
* SequentialSymptomSyndrome: In ''Terror Castle'', right after Jupiter recites the order of sensations/emotions past visitors to the castle went through before fleeing it, Pete sees the PortraitPaintingPeephole and starts going through them in the same order.
* SeriesContinuityError:
** In the early book ''Green Ghost'', Arthur stated that the mansion of Matthias Green had been built "60 or 70 years ago, before Rocky Beach was a town or had a library." However, in the later book ''Phantom Lake'', William Arden tells of the pirate treasure hidden by Angus Gunn when he settled in Rocky Beach in...1872, well before Green's time since the ''Argyll Queen'' was supposed to have sunk "a hundred years ago." While it is true most of the places the boys had to go in the narrative to find out about Laura's surprise were ones that would have existed apart from Rocky Beach (Powder Gulch, Cabrillo Island, Santa Barbara), and it's entirely possible Gunn built his lodge out in what was then virgin countryside, the Ortega stoneyard seems like the sort of place which would require a town of some sort, at least for their main office. There is, however, a possible reconciliation for this discrepancy.[[labelnote:Explanation]]''Green Ghost'' didn't say Rocky Beach didn't exist ''at all'' before 60-70 years ago, just that it wasn't a town and didn't have a library. It could very well have been as small as Powder Gulch, and thus not been officially incorporated, but still had a place like the Ortega stoneyard (a business which a new and growing town would certainly need). It would also still have had a sheriff (to hunt down and kill the Captain and his men, and to investigate Gunn's journal). Also the publication dates of the books shed a little more light--''Green Ghost'' came out in 1965 (thus putting 60 or 70 years ago to right around the turn of the century, an appropriate time for Green to have fled China after running his merchant trade there) while ''Phantom Lake'' came out in 1973. If it is assumed the stories take place in the years they were published (ignoring the fact the boys never age), that's an eight-year difference, meaning there's only a gap of about twenty-eight years between Gunn's time and Green's. In that time it's possible Rocky Beach still hadn't grown enough to become a town or have a library, so that Green's mansion could still be isolated out in the wilderness the way it was described in the backstory.[[/labelnote]]
** While Pete's film knowledge waxes and wanes throughout the books, it seems to be something Brandel missed entirely in his research for the series, since in ''Rogues' Reunion'' Pete not only expresses eagerness to "see what goes on behind the scenes at a movie studio" (even if he's never visited one personally, his father has to have told him a great deal about it already and he reveals plenty of behind-the-scenes knowledge in ''Nervous Lion''--anyway, nothing in the text suggests he already knows anything), but he later asks Jupe why it's called a "sound stage", something he ''absolutely'' should know since his father is a sound man as well as a special effects designer.
* SesquipedalianLoquaciousness: Jupiter sometimes falls into this habit.
* SesquipedalianSmith: Jupiter Jones
* ShaggyDogStory: After a story revolving around two men going to a great deal of trouble (kidnapping and ransom on one side, leaving a mysterious secret message for his daughter on the other) to either gain access to a lost emerald mine or retain possession of it, it turns out in ''Cranky Collector'' that [[{{Irony}} the mine in question had been found long ago by the authorities]] and was being worked by a regular mining corporation. So in the end it was all for nothing.
** Other examples, if not quite so undercutting, are ''Green Ghost'' where the Ghost Pearls end up destroyed (but Mr. Won just might still get their dust, and Verdant Valley still gets saved) and ''Shrinking House'' where the lost Fortunard [[spoiler:turns out to be a fake--but a collector of forgeries still ends up paying a lot of money for it, helping out the Carswells]].
* SherlockScan: Jupiter does this a few times, often when using a clue to deduce connections between suspects and the crime. [[DeadpanSnarker Mocked by Bob]] on at least one occasion, in ''Magic Circle'', when they [[ContrivedCoincidence happen to find]] the matchbook incriminating [[spoiler:Harold Thomas]].
* ShipTease:
** Between Jupiter and Allie, if their SlapSlapKiss relationship (minus the kissing) is any indication. Perhaps a natural progression of putting two know-it-alls together.
** The German version has HandicappedBadass and [[TheSnarkKnight queen of snark]] [[TeenGenius Jelena]] with Jupiter. Her intelligence actually rivaling Jupiter's, one would have to be excused in thinking the [[SnarkToSnarkCombat snarkfest]] that occurs whenever they meet might be [[BelligerentSexualTension something else]]. [[DoesThisRemindYouOfAnything One could say]] [[{{Expy}} she's]] [[SherlockHolmes 'the woman']] for Jupe. She's also good friends with Bob; however their relationship is much more [[LikeBrotherAndSister amicable.]]
** And then there's FanPreferredCouple [[HoYay Peter/Bob]] who [[VitriolicBestBuds bicker]] LikeAnOldMarriedCouple at all times, have something dangerously close to SlapSlapKiss going on, and receive TONS of ship tease in the audio adaptation. [[ShipperOnDeck It helps that the voice actors ship it.....]]
* ShoutOut:
** In ''Green Ghost'', Jupiter references the "curious incident of the dog in the nighttime" from [[Literature/SherlockHolmes "Silver Blaze"]], and it applies in exactly the same way--what is notable is that the dog did nothing in the nighttime, in this case because [[spoiler:there was no actual ghost for it to sense and react to]].
** There's a Creator/JohnDicksonCarr story where a killer hides a glass knife by dropping it into a jug of water. This was referenced in ''The Mystery of the Invisible Dog'' where [[spoiler:a glass statue is hidden in a swimming pool]]. Jupiter Jones figures it out by remembering the Carr story. See HiddenInPlainSight.
** In ''The Mystery of the Laughing Shadow'', no one who hears the eponymous shadow's laugh can identify it or describe it, and in fact it sounds different to everyone who hears it. This is a reference to Poe's "Literature/TheMurdersInTheRueMorgue" where no one could identify the language of the murderer because [[spoiler:he wasn't speaking one at all, being an orangutan]]. Jupiter again references the parallel, and it is apt since the shadow's laugh is actually made by [[spoiler:a kookaburra, thus identifying the resident [[EvilBrit Evil Aussie]] as the BigBad]].
** In ''The Mystery of the Fiery Eye'', Jupe deduces that the eponymous jewel is hidden in one of a series of plaster busts based on the fact their owner had been a Sherlock Holmes fan and one story, ''The Adventure of the Six Napoleons'', had a valuable object hidden in similar fashion. [[spoiler:The whole line of investigation, though, [[IncrediblyLamePun turns out to be a bust]], since it's a RedHerring.]]
** When seeking the money Spike Neely stole from a bank in ''Talking Skull'', Bob suggests he pasted the money on the wall of his sister's home since he had put up new wallpaper for her while he was there. Jupiter mentions this is similar to a Robert Barr story ("The Triumph of Eugene Valmont") where one Lord Chizelrigg hides his fortune in gold by beating it into gold-leaf and pasting it under his wallpaper. [[spoiler:Like the ''Fiery Eye'' example, this also turns out to be a RedHerring since the money is actually hidden under the attic floor; as Jupe points out, pasting paper money to a wall would simply ruin it, unlike gold-leaf.]]
** Bob mentions, when they are discussing the possible hiding places of Angus Gunn's PirateBooty in ''Phantom Lake'', that it could be hidden right in front of their face, something they look at all the time but never even notice or think about, like the purloined letter of Poe. [[spoiler:He's absolutely right too, since the hiding place for the treasure is the lake itself, or its island anyway.]]
** Robert Arthur did a ShoutOut to himself in ''Silver Spider'': when the time came for Jupe, Bob, and Rudy to escape from the dungeon with a TheGuardsMustBeCrazy plot (specifically, the sick prisoner ploy), Jupe offered an idea he'd read in a story from an Alfred Hitchcock collection, that of making ropes from torn sheets, with nooses at each end, and slipping them over the guards' ankles and necks so that, the more they struggled to get free, the tighter they became entangled with each other. Said plot is indeed from an Alfred Hitchcock book, specifically his "Solve-Them-Yourself Mysteries"--and it was written by Robert Arthur.
** ''Silver Spider'' also contains a religious ShoutOut: in the backstory of Varania's Prince Paul, it's revealed that the reason he made the spider a protected creature (and his personal symbol) was because while fleeing from revolutionaries, he went to hide in an attic, and a spider there formed a web over the door so that when the revolutionaries searched the house, they assumed no one had been in the attic in a long time since they’d have to have torn through the cobweb to get in, and so his life was spared. This is nearly identical to a story about [[Literature/TheBible King Saul and David]], as well as one told of [[UsefulNotes/TheProphetMuhammad Muhammad]].
** In ''Blazing Cliffs'', Jupiter mentions the ''Radio/WarOfTheWorlds'' broadcast (and the UrbanLegend surrounding it) when discussing the alien invasion hoax the boys are trying to expose as an example of how easily such a thing can be faked, and how easy it is to take in someone who wants to be fooled on some level. When describing how the UFO could have been fashioned, he also references weather balloons, which is generally the RealLife explanation given for the [[RoswellThatEndsWell Roswell incident]]. Lastly, some of the beliefs Mrs. Barron has about the aliens are rather reminiscent of a number of RealLife {{Cult}}s, particularly Heaven's Gate, although thankfully lacking the suicidal tendencies.
** A former great in Hollywood, living in a forgotten, overgrown mansion...constantly reliving their GloryDays before [[WhiteDwarfStarlet they lost all of their prestige, notoriety, and fame]]...lashing out at [[HorribleHollywood the directors, studio execs, and actors who either abandoned them, used them, or robbed them for their own careers]]...plotting secretly to make a huge comeback, restore their glamour, and show all those who sneered at them... This backstory for the villain in ''Rogues' Reunion'' sounds a very great deal like the plot of ''Film/SunsetBoulevard''. (And the namesake street actually plays a role in the book's plot, since it's where the studio lot and headquarters are located, and where a clandestine rendezvous by the villains takes place.) Except here it's inverted. [[labelnote:Explanation]][[spoiler:It's the director, not the actress, who is living in the past, bemoaning the betrayal of the studio system and the public, and believing he can still get the recognition he deserves; the actress actually wants nothing more to do with Hollywood and the director wants to force her into it because he "discovered" her and thinks he can make her great in order to prop himself up as a genius;]] and instead of a murder, the crimes the villain is implicated in are fraud and kidnapping (although a gun is involved and comes close to being used). It's as if Brandel took the film's RedHerring with [[spoiler:Max]], amped up his behind-the-scenes ManipulativeBastard tendencies, had him buy even more into the false narrative (as he did in the Webber musical), and then made him the outright villain and [[spoiler:Norma]] a complete innocent dupe in the matter. In the end [[spoiler:Lomax]] still has the SanitySlippage Norma Desmond famously experienced (the part where [[spoiler:he starts ordering the boys and 'Bonehead' around as if they were cameramen and crew, which has shades of him thinking they actually are, or that there are imaginary ones nearby to film his great triumph]], is rather chilling, as is his breakdown after they free Peggy), and he even ends up placed in the mental wing of a retirement home for old Hollywood actors and directors.[[/labelnote]]
* ShoutOutToShakespeare: Aside from the usage of Hamlet's soliloquy in ''Stuttering Parrot'', there's the identity of Puck[[spoiler:/Robin Goodfellow]] in ''Magic Circle'' and the quote from ''Theatre/{{Macbeth}}'' in ''Dead Man's Riddle''. Also, Jupiter's uncle's full name is ''Titus Andronicus'' Jones.
* {{Sidekick}}: In many of the books, the boys have one of these in the form of their client, a local who happens to make a handy guide or MrExposition, or a relative who either is seeking a lost heirloom/treasure or wishes help to ClearTheirName or that of a member of their family. A RunningGag early on is that this would be a boy of a new nationality for each book--Carlos from ''Stuttering Parrot'', Hamid from ''Whispering Mummy'', Chang from ''Green Ghost'', Taro from ''Vanishing Treasure'', Chris from ''Skeleton Island'', August August from ''Fiery Eye'', and Djaro from ''Silver Spider''. This gag was dropped for a while, although sidekicks continued in ''Screaming Clock'', ''Crooked Cat'', ''Flaming Footprints'', ''Nervous Lion'', ''Singing Serpent'' ([[DistaffCounterpart this time a girl!]]), and ''Shrinking House'', then was briefly resurrected for Cluny of ''Phantom Lake'' (well, Scottish-American, but close enough), Diego of ''Headless Horse'', and Ian Carew (although only appearing briefly in-story) of ''Deadly Double''. A number of these were found in and around Rocky Beach, justified by its proximity to both Los Angeles and Hollywood. Interestingly, none of these were reckless (at least no more so than the boys themselves) and many were quite helpful.
** Amusingly, once the sidekick in question was their thirty-year-old publisher boss who was also their client (''Magic Circle''). They are also assisted by the studio chauffeur Gordon Harker in ''Rogues' Reunion'' who ends up saving the day against [[spoiler:Lomax]].
* SomethingCompletelyDifferent:
** Every once in a while the usual formula of a client coming to the boys or them stumbling upon a case would be subverted--when, for example, [[BusmansHoliday they happened to be traveling outside Rocky Beach or had been invited away/on vacation]] (''Skeleton Island'', ''Moaning Cave'', ''Monster Mountain'', ''Death Trap Mine'', ''Shark Reef'', ''Blazing Cliffs'', ''Wandering Cave Man'', ''Missing Mermaid''), and once they even ended up traveling to another ([[{{Ruritania}} fictional]]) country (''Silver Spider'').
** The early book ''Whispering Mummy'' has an unusual moment where the action and POV switch to Professor Yarborough and his butler Wilkins as a HowWeGotHere to explain the case of Ra-Orkon and how the professor happened to send a letter to Hitchcock which the boys had just read in the previous chapter.
** ''Trail of Terror'' is extremely different from the usual case. Aside from the fact it's about a road trip cross-country where [[MinimalistCast the only consistent characters are the boys, Pete's grandfather, and the villains]], it also involves: Pete's mother being the one to hire the boys (to keep her father out of trouble); a BusmansHoliday writ large; the boys not even believing there ''is'' a case for some time due to chalking everything up to Mr. Peck's paranoia, eccentricity, and possible senility; it being the first time they become involved in something that threatens national security; and the fact that instead of there being a secret villain they have to expose and unmask along the way to stopping a crime/finding a hidden treasure, the villain is known (or at least revealed to be extremely suspicious) from very early on--instead the entire case/book consists of simply trying to prove his villainy, keep him from obtaining the evidence of his crime, and get him arrested, all while being chased by him and his spy contact.
* SpeechImpediment: How the Investigators figure out where the BankRobbery money in ''Talking Skull'' is hidden--because the criminal who hid it couldn't pronounce the letter 'L', he was able to use a green stamp (representing the money) under a four-cent stamp to tell them it was [[spoiler:under the ''floor'' of the house]].
* SpellMyNameWithAnS: Huganay/Hugenay.
* SpoilerCover: A few of the covers of the books also spoil major plot points or even endings. ''Vanishing Treasure'' depicts the boys with the belt in Headquarters, revealing they get it back; ''Fiery Eye'' shows them digging the eponymous jewel up, thus completely deflating the tension of the search for the busts; ''Silver Spider'' shows the eponymous spider [[spoiler:in a web]]; one version of ''Laughing Shadow'' shows Indian Head Mountain, thus hinting at [[spoiler:the meaning of "eye of the sky"]] before it is revealed; ''Coughing Dragon'' makes it fairly clear that said dragon is [[spoiler:a robot]]; and a very eagle-eyed observer will notice [[spoiler:the awning patch with the stripes going the wrong way]] on the eponymous ''Shrinking House''.
* SpotTheImpostor: Variation, where it's heroes trying to fool villains--when the kidnappers in ''Deadly Double'' catch him and Ian together, Jupiter thinks fast and, using his [[ChekhovsSkill well-established acting/mimic abilities]], imitates Ian's Nandan accent. Helped along by Ian pretending to be him, and Bob and Pete each identifying different boys as Ian, so that the kidnappers are completely, and rather humorously, confused. Things quickly stop being funny, however, when the kidnappers decide to take both of them until they can find someone to identify Ian conclusively.
* SpottingTheThread: Often used to catch the villain (or catch him in a lie), such as when the fake El Diablo in ''Moaning Cave'' was revealed to be [[spoiler:Professor Walsh]] by the fact he [[spoiler:held his gun in his left hand]], or in ''Sinister Scarecrow'' when things like knowing about the crystal-hung candelabra on the museum staircase landing and somehow getting down the box of photographs from the closet shelf revealed that [[spoiler:[[ObfuscatingDisability Mrs. Chumley could walk]]]]. But on at least one occasion it was a RedHerring--after having chased the villain into the barranca in ''Shrinking House'' and knowing he'd injured himself falling in, the boys looked for a limp to identify him later. But [[spoiler:[=DeGroot=]'s limp turned out to be from an old injury, and he wasn't even a villain.]]
** In two cases the villain in question [[GenreSavvy was aware]] of the 'thread' and took pains to conceal it, but Jupiter managed to catch him with it anyway--in ''Two-Toed Pigeon'' Blinky knows very well his eye tic will give him away, so he covers it with sunglasses but [[spoiler:the fact Frisbee never wears them, and Blinky wears them even at night]] gives away he's an impostor and what his real identity is, and in ''Rogues' Reunion'' [[spoiler:the fake Bonehead's attempt to cover his ears with his hair is undone by the wind when he rides in his convertible with the top down]].
* StartXToStopX: In order to undo the "{{Curse}}" placed on Allie's aunt by a con man in ''Singing Serpent'' (because YourMindMakesItReal), the boys bring in...a con woman of their own, portraying a gypsy who can "break" it.
* StrawVegetarian: Mr. Smathers of ''Monster Mountain''. He's a bit more sympathetic than most examples; isn't weak, repressed and secretly desiring meat, or wishing all humans to be killed (in fact he's a pacifist); and the fact he turns out to be in the right and not an EvilVegetarian is a sign the author actually agreed with his views but unfortunately overdid the depiction into caricature. But he's certainly quite strident in his views, pushes them on others, and has a rose-tinted view toward animals--though this may be slightly justified since he seems to be a genuine FriendToAllLivingThings.
** Mr. Harris of ''Laughing Shadow'' is an even stronger example of this trope. [[spoiler:As well as an EvilVegetarian who, thanks to being a ConMan, is also a hypocrite since he's actually a regular meat-eater in disguise.]]
* SundialWaypoint:
** Used to find the eponymous ''Fiery Eye''. Notable in that the waypoint is a mountain overlooking a canyon actually ''named'' (Sun)Dial Canyon.
** Although not seen directly in-story, it's revealed at the end of ''Cranky Collector'' that Pilcher's mysterious message leading to the lost emerald mine also contained a reference to one of these, in this case a certain peak in the Andes called Old Woman.
* SwappedRoles: This happened in the {{Backstory}} for ''Shark Reef'': Shozo Yamura, grandfather to Torao, ended up switching places with his 'friend', criminal and juvenile delinquent Hideo Gonda, so as to go out to sea on a submarine and serve patriotically rather than be stuck in a safe desk job. When said submarine sunk, Gonda took the opportunity to swap his records and fingerprints with those of Yamura, and thanks to the family's records being lost in Hiroshima and the excuse of injuries, memory loss, and eight years away, he was able to pass himself off as Yamura, thereby taking over the family company and fortune. Torao's whole plot is to reveal this truth and [[SetRightWhatOnceWentWrong set the record straight]] so Gonda can be put away and his family's reputation, money, and company restored.
* SwordCane: Three-Dots has one in ''Fiery Eye'', which he uses to quite the chilling effect on the boys.
[[/folder]]

[[folder: Tropes T-Z]]
* TeenGenius: Jupiter Jones. He has the general knowledge of an educated adult, often comes up with ingenious ploys, frequently builds technical gadgetry from scratch, and besides is a skilled actor. Stated to be something he developed through constant reading and research specifically to counteract his aversion to [[AllOfTheOtherReindeer being mocked and laughed at for his weight]].
* TelecomTree: Known as the Ghost-to-Ghost Hookup.
* ThemeNaming:
** The various entrances to the salvage yard and to Headquarters all follow one of two themes: AddedAlliterativeAppeal (Green Gate One, Red Gate Rover, Tunnel Two) or RhymesOnADime (Easy Three, Dour Foor). A numbering system is also included in the names, naturally.
** A couple of the books had chapter titles which were {{Shout Out}}s to other media, usually famous films. ''Creep-Show Crooks'' especially used these, since it included "The Girl With a Thousand Faces (in reference to the Lon Chaney biopic, also referenced in the very first book ''Terror Castle'' through Stephen Terrill's sobriquet), "Dracula Lives Again" (the Marvel comic), "Chamber of Horrors", and "Escape to Nowhere." Two Hitchcock films (naturally) are also referenced: also in ''Creep-Show Crooks'', "The Lady Vanishes"; and "The Man Who Knew Too Much" in ''Rogues' Reunion'' (which is lampshaded by Jupiter).
* ThirteenIsUnlucky: Invoked by Hitchcock in his introduction to ''Crooked Cat'', wherein he notes the extreme difficulties, turns of bad luck, numerous accidents at the carnival, and other dangers that assault the boys which they might have avoided, or at least been better prepared for, if they'd been wary of taking on their thirteenth case. (Also note the case involves [[SuperstitionEpisode looking for a stuffed cat which, though striped, is mostly black]].)
* ThisIsReality: Crops up every once in a while, such as in ''Fiery Eye'' when Jupiter is tied up by the villains and thinks, "In stories, when someone was tied up there was always a convenient way to get loose....But he had nothing." In ''Scar-Faced Beggar'', when Pete starts theorizing about Ernie being a foreign agent and the blind beggar his contact (which is quite close to the truth), Bob dismisses him with "[[YouWatchTooMuchX you watch too much TV]], in real life people don't act like that." Interestingly, Jupiter then responds that [[FreakierThanFiction people behave in ways that are even more fantastic]] [[RealityIsUnrealistic in real life]].
* ThoseTwoGuys: Hans and Konrad, the Bavarian brothers who work as helpers in the Jones Salvage Yard. Often called upon to be TheCavalry or BigDamnHeroes because each of them is his own OneManArmy. Otherwise they remain OutOfFocus background characters, although they did get ADayInTheLimelight in ''Monster Mountain''.
* TitleDrop: Variation. Other than when the case name is mentioned by or to Hitchcock during the ending summation, and when the title refers to a place, it is otherwise never mentioned directly in the books. However there is usually at least one scene where the item or thing in question is referenced or described, with the unique trait or appended adjective mentioned (the parrot that stutters, the mummy that whispers, the clock that screams, the laughing shadow, the lion that's nervous, the headless horse, a scarecrow that's sinister, and so on). On one occasion however--the very first book!--Jupiter actually declares they must solve "the secret of Terror Castle".
* UsefulNotes/{{Trademark}}: The three question marks on the Three Investigators' business card, standing for "questions unanswered, riddles unsolved, enigmas unexplained" and similar verbiage and designed by Jupiter to make people ask about their significance, and stand out in their minds. It works.
* TreacherousAdvisor: [[spoiler:Professor Shay of ''Phantom Lake''.]]
* TrickAndFollowPloy: Used at various points by the boys to get the villains to lead them to the treasure/loot/clue/hiding place they seek. It backfires once in ''Scar-Faced Beggar'' though, since the villain is clever enough to realize he was being followed and backtracks to circle behind; so although Jupe and Pete find where the Denicolas and Bob are being held, they also get captured themselves.
* TwoLinesNoWaiting: Occasionally a book will have multiple plotlines/cases, and quite often they intersect. In at least two books the lines literally intersected, with [[spoiler:the midgets]] of ''Vanishing Treasure'' being responsible for the stolen belt, the "gnomes", and the bank robbery, and with [[spoiler:Harold Thomas]] of ''Magic Circle'' responsible for the fire, the theft of the manuscript, and the theft of the films (albeit by working for two different criminals).
** Verges into ThreeLinesSomeWaiting in ''Missing Mermaid'' where, as [[LampshadeHanging the book's very blurb makes note of]], there are so many apparent mysteries (the broken statue, the supposed haunting of the inn, Mooch's dog reward scheme, the slave market) that the boys keep getting distracted from their search for the missing Todd Stratten. However even in this case all the mysteries end up intertwining or being relevant in some way, even the haunting (which [[spoiler:Clark Burton]] is using to keep people from investigating the inn and finding his secret room, though it's otherwise a RedHerring). Another example would be ''Scar-Faced Beggar'' which, aside from the beggar, involves a bank robbery, Hector Sebastian as a RedHerring suspect, a boat-rental business, a rally for patriotic rebels of a South American country being held at a condemned hotel, a makeup artist, a woman with psychic dreams, and terrorist gunrunners; again, it all ends up being relevant (except for Hector Sebastian, which is just a set-up for him to become the boys' new mentor).
* UncattyResemblance: In ''Sinister Scarecrow'', Jupiter think the entomologist Dr. Woolley looks rather like an ant himself with his bald head and large bugging eyes; [[SugarWiki/FunnyMoments he even starts staring at his forehead, thinking antennae will grow, making Dr. Woolley ask him if he had something on his forehead]].
* UndeadAuthor: Touched on briefly in ''Moaning Cave'' when the boys learn of the legend of the Old One--supposedly no one has ever survived encountering it (and it's invisible, too), yet somehow the legends are still able to say it is black and shiny. When Pete asks about this, Mrs. Dalton laughs and agrees, but also suggests perhaps someone once saw it, told everyone else, and that's how its appearance could be known even if no one later saw it.
* VehicularSabotage: Happens three times where the boys use it to stop a villain's pursuit or escape--in ''Shrinking House'' Bob removes the ignition wires from [=DeGroot=]'s car, in ''Dead Man's Riddle'' Billy takes the distributor cap off of Turk and Savo's car, and in ''Magic Circle'' Pete removes the ignition wires from every one of the villains' cars after they arrive at Madeline Bainbridge's estate. He doesn't count on one of them fleeing in Beefy's car however (which still had the key in the ignition). An unusual variation also occurs in ''Trail of Terror'', in which the boys sabotage a motorcycle belonging to a biker gang harassing them...so that when the gang goes to pursue them, its front wheel falls off.
* VillainTakesAnInterest: In ''Vanishing Treasure'', thanks to admiring Jupiter's intelligence, Rawley keeps offering to take him on as a criminal apprentice. Hugenay makes a similar offer in ''Screaming Clock''.
* VillainTeamUp: In ''Sinister Scarecrow'', thanks to {{Blackmail}}. The more usual version (for money and/or equally criminal desires) appears in ''Vanishing Treasure'' and ''Magic Circle''. Another version resulting from {{Blackmail}} is in ''Wreckers' Rock'', in which Sam Ragnarson joins up with the Gruber brothers [[spoiler:and William Manning]] to aid in their InsuranceFraud scam, since he concludes this is a better source of money than digging for lost gold. It doesn't turn out too well for him.
* WellDoneSonGuy: Jim Clay of ''Dancing Devil'' turns out to be this [[spoiler:and it's why he pretends to destroy the Dancing Devil, so his father can keep the thing he treasures so much]]. William Margon of ''Smashing Glass'' claims to be this (his actions being done "just to make you proud") but his father calls him on it, saying he instead wanted to impress him, make money, and be important.
* WhatHappenedToTheMouse:
** After the events of ''Stuttering Parrot'', an afterword by Alfred Hitchcock stated that the young Mexican boy Carlos was taken under Worthington's wing, gotten a job washing and cleaning the cars at the Rent 'n' Ride Auto Rental Agency, and allowed to live with the Joneses, earning room and board by helping at the salvage yard. But the reader never sees or hears from him again in any of the later books. Additionally, the mynah bird Blackbeard is adopted by the boys as a sort of mascot for the Three Investigators, but after a few brief appearances he too vanished from the series--even from the books written by Arthur.
*** At least in the case of "Blacky" the German version subverts this, with the bird being a staple of both the book series and its audio adaptation, where its iconic screech can be heard in almost every episode. He even gets his own [[ADayInTheLimelight day in the limelight]] when he is abducted.
** In ''Fiery Eye'', Bob meets a girl named Liz Logan whose mother has the bust of Octavian they believe holds the jewel. In the process of helping him get it back, she speaks eagerly of wanting to be an investigator too and offers Bob her help if they ever need a girl to assist them in ways a boy couldn't. Bob promises to let her know if such an event ever happens, but despite him seeming genuinely interested in her offer (and not just brushing it and her off as annoying, as Jupe or Pete might), this is never brought up to the others and she never appears in the series again--though she may have planted the seed for Allie in ''Singing Serpent''. WordOfGod has stated that Liz was based on Arthur's own daughter Elizabeth, and that the reason she never appeared in the series again was because Elizabeth decided [[PluckyGirl "the best way to become a girl operative was to grow up to write stories herself."]] (And she did.)
* [[WhatsASecretFour What's a Secret Four?]]: The boys' junkyard-based hideout has a large number of code-named entrances (Green Gate One, Red Gate Rover, etc.). Every mentioned path or doorway was used in at least one of the stories, except for "Secret Four". Although Arthur did mention very early on that there were supposed to be four entrances through the salvage yard fence, but the only ones we ever see are Green Gate One and Red Gate Rover; no later author followed up on this, and in fact in ''Singing Serpent'' when Allie has figured out the location of Red Gate Rover and uses it to blackmail the boys into letting her hire them, they speak of building other entrances to replace it. So apparently these others have been {{Retcon}}ned out of existence.
* [[WhereTheHellIsSpringfield Where the Hell is Rocky Beach?]]: Unlike most examples of this trope, the location of the fictional Rocky Beach is actually fairly easily guessed due to the specific details of landmarks and distance to other California cities. One fansite has pinpointed it to either Topanga Beach or Ocean Park, California, both within the right distance range of Hollywood, Santa Monica, and Los Angeles.
* {{Wicca}}: Appears in ''Magic Circle'', and depicted with [[FairForItsDay a fair amount of accuracy for the times]]. One of many examples of M. V. Carey having [[ShownTheirWork Shown Her Work]] due to her fascination with the supernatural.
* WigDressAccent: The PaperThinDisguise worn by the gang working for [[KnownOnlyByTheirNickname Three-Dots]] in ''Fiery Eye'' consists of...fake mustaches and horn-rimmed glasses.
** [[spoiler:Java Jim of ''Phantom Lake'' turns out to be this crossed with either LatexPerfection or ExpressiveMask.]]
* WorkingTheSameCase: Two examples, both early in the series--in ''Whispering Mummy'' Pete, fed up with the seemingly supernatural case, decides to go off on his own to investigate a missing cat, only to find out it connects to the mummy. Then in ''Vanishing Treasure'' the bank robbery being performed by the "gnomes" they investigate turns out to be perpetrated by the same thieves who stole the Emperor's belt from the museum which had forbidden them from getting involved ([[NotNowKiddo because they were "just kids"]]).
* WritingIndentationClue: Subverted. In ''Sinister Scarecrow'' when Jupiter finds a newspaper and scratch pad near the kitchen phone after the museum robbery, it looks like he's going to use this method to find out what was written there...except [[IdiotBall the thieves didn't bother to throw out the newspaper or the pages in the scratch pad]], so the phone number of a shipping company, the name of the ship they were going to escape on, and even [[spoiler:the word Vermeer, referencing the painting Mrs. Chumley always wanted]] were right there to be found.
* WrittenByTheWinners: The {{Aesop}} of ''Headless Horse'', as referenced by both Hitchcock and Jupiter. The three soldiers who, in their greed, decided to steal the Cortes Sword from Don Sebastian Alvaro made up a fake weapons-smuggling, fake breakout, and fake death for their prisoner, then deserted to pursue him; their report on this is what entered the history books and, without any other documentation or information to contradict, it was believed to be the truth not only by the Army but by Don Sebastian's son Jose. [[spoiler:Helped by the fact that [[MutualKill both]] Alvaro and [[LaserGuidedKarma the deserters]] died, so that no one remained who could tell what really happened.]]
* YellowPeril: Mr. Won of ''Green Ghost''.
* YouMeddlingKids: The villain of ''Crooked Cat'' comes ''this'' close to saying the trope name when caught! ("I'd have got away except for those stupid kids!") Few others do, though a number of them are certainly enraged or have [[VillainousBreakdown breakdowns]] due to being caught by teenage detectives.
* YourPrincessIsInAnotherCastle: Fairly frequent, when either the lost item they're searching for literally does turn out to be somewhere else or they encounter a RedHerring. One particularly memorable example is in ''Stuttering Parrot'' when, after following every clue to the Merita Valley graveyard, they discover the long flat box which had once held the painting holding only a note saying, essentially, "[[ThisLoserIsYou You didn't read the clues well enough, better luck next time!]]" The last parrot clue, "I never give a sucker an even break, and that's a lead pipe cinch!" even lampshades this...[[spoiler:[[SubvertedTrope until it turns out]] it was actually a stealth clue telling them the lead pipe found in the graveyard is the real hiding place for the painting]]. Another example in ''Fiery Eye'', almost a comedy of errors, not only involves them looking in the wrong bust for the jewel, but finding a FakinMacGuffin version of it, followed by looking in the right bust after ''it'' got [[StolenMacguffinReveal mistakenly switched]] with one that the villains stole but only finding another note telling them to "delve deeper". Still another example occurs with [[{{Troll}} Dingo Towne]] and the fake stash of gems in ''Dead Man's Riddle''.
* YourTerroristsAreOurFreedomFighters: Forms the backstory and motivation of the villains in ''Scar-Faced Beggar''.
[[/folder]]
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