History Literature / TheThreeInvestigators

* UsefulNotes/BritishEnglish: The puzzle of ''Dead Man's Riddle'' is written entirely in Cockney rhyming slang.

* 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.

** 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.

* HarmfulToMinors: Some of the things the boys get into are genuienly dangerous. All three boys have been kidnapped, held hostage, been in more than one plane crash, gotten held at gunpoint, and more. Pete has even gone into cardiac arrest and almost died had he not been successfully resuscitated. At a certain point, their parents and guardians have become savvy to their dangerous antics and started warning them to tone down the detective work (which never works).

* SpellMyNameWithAnS: Huganay/Hugenay.

* TelecomTree: Known as the Ghost-to-Ghost Hookup.

* 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.

** Anything after the original series. Crimebusters already amped up the action and even had some instances of blood (like when Pete's hands were strung too tight in ''Show Reel'' causing bleeding and a character literally dying during one of the stories), but the German Extended series took it even ''further''. Injuries and blood is liberally used when applicable, sliced open wounds and even broken bones. Biggest moments include: Jupe [[spoiler:getting shot, though it was only a graze, and breaking his leg in another story]], Bob [[spoiler:getting amnesia and getting into a fight with Pete leading to both parties badly injured and was badly poisoned in another]], Pete [[spoiler:going into cardiac arrest after getting electrocuted and was barely resuscitated through [=CPR=]] and literally getting strapped to a MindRape torture device]].

* 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.

** Exploring 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 are explored in ''Death Trap Mine.''
** The boys are 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.
** In ''The Missing Mermaid'', a five-year-old child vanishes and his beloved pet dog is found dead and stuffed into a dumpster. The boardwalk setting is also surprisingly dark and sleazy at times. The Three investigators witness a drug deal unrelated to the main plot, and an elderly local subtly implies that an associate of their prime suspect is a prostitute.
** 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 fear [[MissingChild regarding Jupiter's kidnapping]], 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.

* AdultFear: Some of the things the boys get into is genuienly dangerous. All three boys have been kidnapped, held hostage, been in more than one plane crash, gotten held at gunpoint, and more. Pete has even gone into cardiac arrest and almost died had he not been successful resuscitated. At a certain point, their parents and guardians have become savvy to their dangerous antics and started warning them to tone down the detective work (which never works).

%% * GettingCrapPastThe Radar: Due to overwhelming and persistent misuse, GCPTR is on-page examples only until 01 June 2021. If you are reading this in the future, please check the trope page to make sure your example fits the current definition.

* LiteralMetaphor: In ''Invisible Dog'', Jupiter invents a special ointment that when it comes in contact with human skin will over time cause it to (temporarily) turn black; this, in lieu of fingerprints, will allow them to discover just who is entering Mr. Prentice's apartment and moving things around, since he places it on various handles and knobs. The end result is the person breaking in (a nosy landlady, it turns out, who secretly had a key made) ends up with "the guilty stains" on their fingers--i.e., she's caught red (or black) handed--and because it won't wash off by normal means she's even seen [[OutDamnedSpot constantly rubbing and wiping her hands]] when they confront her.

*** Meanwhile, the saddle-tramp cowboys of ''Headless Horse'' make a campfire on the Norris Ranch, and thanks to the wind sparks get carried and cause a wildfire that endangers both that ranch and the Alvaro Ranch, requiring numerous characters from both ranches (and of course the county and local fire departments) to work together to douse it. Thankfully their work plus a timely rainstorm helps save the day, but the resultant burned land isn't able to hold water later when the rains don't stop, leading to catastrophic flooding and mudslides. Unfortunately, sparks also seem to get carried to the Alvaro Ranch, destroying both the barn and the hacienda...but this turns out to have been deliberately set by the same saddle-tramp cowboys, who overheard ranch manager Cody [[RhetoricalRequestBlunder complain about wanting to claim the Alvaro Ranch for his boss Mr. Norris]] and [[StopHelpingMe thought this would help]]. Too bad for them this act destroys the Alvaros' antiques they were going to sell to Uncle Titus, thus getting the boys even more invested in the plot, and that [[IdiotBall they accidentally left behind]] a set of keys Cody gave them to [[SignatureItemClue the Norris ranch wagon]].

* [[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''.

** ''Wandering Cave Man'' is slightly better— the culprit ''does'' disguise themself as a caveman wearing animal skins and frighten people who see him, but the boys themselves never see him dressed like this.

* 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.

* 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.

* FriendlyEnemy: Hugenay again.