* AngstWhatAngst: The three boys have been in some absolutely ''harrowing'' experiences. Getting held up at gunpoint, taken hostage, getting kidnapped, plane crashes, etc, but they don't seem to be bothered by what they experience. At the end of the book, they're usually ready for another mystery-filled adventure with no hang-ups from previous cases (unless it involves a nemesis, Victor Hugenay for Jupe or Clarissa Franklin for Bob).
** Only Pete shows signs of any reluctance to taking on more dangerous cases and it's more due to his status as a CowardlyLion than it is from trauma. Even then, he's experienced arguably the most terrible things throughout the series history (i.e. getting accidentally sent to an island in Micronesia on his own, getting kidnapped and was missing for four days, going into cardiac arrest via electrocution), yet the potential trauma from those situations never comes up.
* {{Anvilicious}}: Thanks to the time period, it's not at all surprising that this would occur, and Marc Brandel being a clear animal lover is quite commendable, but [[AuthorTract some of the praise given to whales]] in ''Kidnapped Whale'' and Fluke's unusual abilities are at times [[{{Glurge}} a bit much to swallow]].
* BaseBreakingCharacter: Allie Jamison. Some praise her for being a rare female main character, as well as competent and humorous and wish she'd appeared more. Others view her as smug and prone to SingleIssueWonk on the case (particularly in the second book she appeared in).
* BizarroEpisode: The episode "Todesflug" (Death Flight) from the German release has achieved somewhat of a cult status in the fandom due to its weirdness. It starts out fairly ordinary, with the Three Investigators being stranded in the desert after their car breaks down on the way to a sci-fi convention. But then it goes completely off the rails and into outright Franchise/JamesBond territory when they stumble across the secret base of a rogue [=NASA=] scientist who has somehow managed to put a [[KillSat satellite-mounted laser cannon]] into orbit, culminating in Bob ''piloting a space shuttle'' in order to disable the satellite (which he [[IKnowMortalKombat learned from a video game]]). Fans are divided on whether the episode is SoBadItsGood or just plain bad, but everyone agrees that it should be [[FanonDiscontinuity treated as non-canonical]] -- and it seems that even the series' writers agree with the fans on this one, since the events of this episode have never been referenced in any of the following installments.
* CharacterRerailment: After Crimebusters had completely overhauled the Investigators' personalities, trying to make them DarkerAndEdgier to appeal to a teenaged crowd (which made them lose some of the personalities that the fan knew them for), the German extended release re-railed the characters back to their original depictions. They still have some of their Crimebuster personalities, but have more or less returned to their original characterizations.
** For Jupiter, his Crimebusters interpretation made him deeply insecure about his appearance and his ability to talk to girls, to the point where every other sentence was him lamenting how 'ugly' he was because he was overweight; becoming extremely jealous of Bob. However, he regains most of his confidence back in the German release and doesn't seem so insecure anymore and had refocused his attention on solving mysteries than girls (though he still had dated and has crushes from time to time). He still gets annoyed when Peter or Bob poke fun at his weight, but reacts in a much less self-deprecating way and more like how his younger self handled it.
** For Bob, in Crimebusters he is often portrayed to have hated his past as a shy, bookwormish kid and complains whenever Jupiter tries to get him to research stuff. He also prioritizes his part-time job and girls more than he does detective work, which makes him completely absent for most of the stories in that era. However, in the German extended release he has slowly returned to some of his original characterization, becoming more involved in cases again and picking up his role again as Records and Research; his [[TheCasanova Casanova]] tendencies are also downplayed and he seems to enjoy DoingResearch again. Eventually, he has become a mix of most of his original characterization and a little of his Crimebusters interpretation.
** As Pete's personality hasn't deviated that much from his original characterization, his character was derailed the least. However, in Crimebusters, he often prioritized Kelly over his detective work and was often described to be hopelessly in love with her, whereas the German extended release had him a little more independent and prioritizing his detective work instead. They have even broken up at times due to Pete being so seemingly busy with being a detective, though they always got back together.
* GeniusBonus: On numerous occasions, Jupiter's intellect and knowledge base allow him to make connections and deductions that most readers in the target demographic wouldn't be familiar with--Shakespeare is the most obvious example, since the famous Hamlet soliloquy quote appears in ''Stuttering Parrot'', while Puck, the pseudonym used by [[spoiler:Harold Thomas]] in ''Magic Circle'', is how Jupiter identifies him as [[spoiler:the missing Charles Goodfellow]]. Anything on the supernatural in the M.V. Carey books actually counts as this, but in general the series authors tend to include all manner of intriguing and informative details in the stories, usually connected in some way to unmasking the criminals or solving the mystery, though not always. Other examples would be:
** "John Silver" from ''Stuttering Parrot'' (and for that matter, the names of all of the parrots).
** The Augustus/Octavian bust mix-up in ''Fiery Eye''.
** The kookaburra from ''Laughing Shadow''.
** Francois Fortunard's lost masterpiece from ''Shrinking House'' (which is based off the missing Franz Marc painting "The Tower of Blue Horses").
** The ''Queen of the South'' in ''Dead Man's Riddle'' (which is clearly the ''Queen Mary'' with the SerialNumbersFiledOff).
** The history of Fremont's expedition in California during the Mexican War in ''Headless Horse''.
** The bit with Indonesia once having been a Dutch colony being how [[spoiler:Harold Thomas]], [[SpottingTheThread who ate at an Indonesian restaurant]], was revealed as Charles Goodfellow, original native of Holland, in ''Magic Circle''.
** The lone UsefulNotes/WorldWarII submarine attack by Japan on the California coast, after Pearl Harbor, which forms the backstory for the hero and villain of ''Shark Reef''.
** Mr. Bonestell of ''Scar-Faced Beggar'', who shares a name with hugely influential astronomy artist Chesley Bonestell (after whom the Association of Science Fiction and Fantasy Artists named their annual awards for artistic achievement, given every year at the World Science Fiction Convention). Appropriate for a book in which psychic dreams turn out to be real.
** The 1907 gold double-eagle coin created by Augustus Saint-Gaudens for the U.S. Mint at the behest of Theodore Roosevelt, the theft of which is one of the drivers of the plot in ''Smashing Glass''.
* GermansLoveDavidHasselhoff: The series is hugely popular in Germany, where several authors have added many books not found in the original American series. (In German, they are called ''Die Drei ???'', which is pronounced ''Die Drei Fragezeichen'', which in turn means ''The Three Question Marks''.) Furthermore, Germans love the AudioAdaptation of ''The Three Investigators''. The voice actors of the three heroes (who were never [[TheOtherDarrin swapped out]], in spite of the audible change from kid to adult voices during the series' run), even can be considered celebrities in their own right. There have been release parties, during which fans meet to hear the newest play, and at this point there have been three stage shows with a fourth one upcoming in 2014. There have also been two German-produced films starring American actors as the trio and filmed in English, with [[CaliforniaDoubling South Africa playing the US]] - ''The Three Investigators and the Secret of Skeleton Island'' (2007) and ''The Three Investigators and the Secret of Terror Castle'' (2009).
** Also the series is so popular that the 2009 stage adaptation of ''Screaming Clock'' drew over 15000 people into the Waldbühne (forest stage) open air amphitheatre in Berlin to listen to the three voice actors play out one of their classic episodes and set the world record for attendance to a single show of a live audio adaptation. In 2014 they managed to break their own record, with an original story written only for the tour and did so by cramming 20000 people into the Waldbühne.
** The movies are very unpopular with the fanbase, though, because the fans felt that they are not true to the source material at all.
* HarsherInHindsight: Thanks to the numerous dangerous and extremely tense events which occur during ''Shark Reef'' (violent protests, kidnapping, a hurricane that nearly destroys the oil platform while Jupe and Pete are aboard, sharks, Gonda basically being a Yakuza-lite), Hitchcock (as the chapter title says) pleads exhaustion. This turns out to be the very last book he ever appears in, as after this is when the RealLife Hitchcock died.
** Pete is overly cautious and claims that his ambition is to 'grow very old'. Come 'Der Meister des Todes', he technically does ''die'' after getting shocked and going into cardiac arrest.
* HoYay: Has it's [[HoYay/TheThreeInvestigators own page]] now.
* MagnificentBastard:
** [[PhantomThief Victor Hugenay]] is a debonair art thief who [[CrypticBackgroundReference once robbed the Louvre]] and shows up in Rocky Beach twice, trying to get his hands on missing paintings. Hugenay is an intelligent man who, unlike other antagonists from the two novels he appears in, avoids showing his hand until he's in a perfect position to take control of the situation. On one occasion, he saves his henchmen from being arrested for ImpersonatingAnOfficer by ensuring that they're wearing the uniforms of a police department on the other side of the continent. Hugenay is quite happy to bask in his own intelligence but is equally impressed and amused whenever Jupiter, Bob, and Pete do something brilliant. Although he fails to get his prize in either of his appearances, in both books, he avoids arrest and [[GracefulLoser is neither angry nor dejected over his loss.]] In his second appearance, Hugenay persuasively convinces Jupiter to join him in an EnemyMine scenario and never betrays the young detective.
** ''The Mystery of the Talking Skull'': [[ConArtist "Smooth" Simpson]] races against both the boys and a trio of hard-boiled thugs to retrieve the missing loot from a bank robbery. Simpson manages to bluff the boys into thinking that he's a bank investigator, enlisting their help in finding the money with the promise of a nonexistent reward. When Simpson's deception is revealed, even Jupiter is caught completely off-guard. When the other criminals capture the four, Simpson apologizes to the boys for putting them in danger and tells Jupiter not to feel bad about falling for his alias. When a group of heroic Romani show up to overpower his kidnappers and free the boys, Simpson quietly escapes his bonds and slips away during the confusion, being the only criminal in the story to avoid being arrested.
** ''The Mystery of the Flaming Footprints'': [[ALighterShadeOfGray General Klas Kaluk]] is a veteran of the revolution which [[TheRevolutionWillNotBeCivilized overthrew and murdered]] the exploitative Azimov dynasty of Lapathia. Lapathia becomes a military dictatorship with Kaluk heading the SecretPolice but develops a noticeably higher standard of living for its people. Decades later, Kaluk is sent to Rocky Beach to retrieve the long-missing crown of the Azimovs from one of their last loyalists, Kaluk's former friend Alexis Kerenov. When Jupiter investigates Kaluk, the general quickly sees through his misdirection and threatens to torture him in a way that makes Jupiter think that he [[TortureTechnician has a lot of experience in that field]]. When he's being held at gunpoint by Alexis, Kaluk calmly convinces Alexis to let him go and to turn over the crown so the people of Lapathia can enjoy it as a museum piece. He also gently chides Alexis for neglecting his family for the dream of restoring a largely exploitative dynasty which could only hope to regain power through violence. Kaluk then leaves gracefully, telling Alexis that he hopes they're friends, and not enemies.
* PostScriptSeason: Although the story is perfectly serviceable, intriguing, and well-written in its own right, ''Cranky Collector'' feels a bit like this in the sense that following as it does after ''Wreckers' Rock'' as the last American volume in the original series makes it feel a bit tacked on. Not only does ''Wreckers' Rock'' include all the great elements of a Three Investigators book (lost treasure, lots of suspects, some great chase scenes and rescues, a ScoobyDooHoax, multiple villains/plot threads, a surprise reveal of a villain and his crime, and the reappearance of the colored chalk after a very long absence from the series), but the ending chapter with Hector Sebastian involves his Vietnamese cook, Hoang Van Don, literally announcing the boys' names and legitimate status as respected investigators on national television (albeit on a cooking show). After publicity and fame like that, anything else would seem a bit anticlimactic, and it would be a great 'ending' for a series that otherwise implies AndTheAdventureContinues.
* RootingForTheEmpire: A few books, like ''Blazing Cliffs,'' have affable or audacious enough villains and/or unpleasant enough targets of the crime that the readers might partially hope the Investigators will fail to foil the crime.
* TheScrappy: Large parts of the fandom regarded the girlfriends introduced in the ''Crimebusters'' era as this, as they [[CreatorsPet would often get undue amounts of focus]], even going so far as to [[TheWorfEffect making it appear that the Investigators themselves were criminally oblivious to what was going on and solving the cases on their own]]. Thus Bob's girlfriend Elizabeth was written out promptly with Jupiter's girlfriend Lys following a bit later. As of today only Peter's girlfriend Kelly remains in the books while all three have been written out of the show.
** [[DieForOurShip Kelly]] gets the worst of this by [[FanPreferredCouple Bob/Peter]] [[YaoiFangirl Shippers]] that read the books. In [[SlashFic fanfictions]] she's largely depicted as a [[AlternativeCharacterInterpretation superficial, shallow, controlling and high maintenance girlfriend]] and is promptly gotten rid of in favour of saintly Bob.
* TheyChangedItNowItSucks: In Germany, two of the boys were renamed to "Justus Jonas" and "Peter Shaw" respectively. When they got the original names for some time, because of legal reasons, this trope happened.
* TheyWastedAPerfectlyGoodCharacter: In ''Kidnapped Whale'', rather than the boys using Worthington and the Rolls-Royce to get around, the character of Pancho is suddenly introduced. He is a Mexican friend of the boys whom they kept out of jail when he was accused of stealing parts from the auto garage where he worked; in gratitude he's often available to take them places when Worthington, or Hans and Konrad, aren't. He's also extremely fascinated by cars in general, not only knowing all about them but capable of assembling new ones from the parts from various models, thus creating unique vehicles that people come from miles around to buy. Now whose background does this sound a great deal like, if we allow for some aging while keeping the trio the same? Carlos, from ''Stuttering Parrot''. The way he is used as a substitute for Worthington is in itself a great idea that keeps the stories from being too repetitive and allows for traveling to different places, but considering Carlos had been fascinated by the Rolls himself, had befriended Worthington, and ended up working for the Rent 'n' Ride Auto Rental Agency, it wouldn't take much of a stretch to imagine he could have ended up owning his own garage in the future where his knowledge and ingenuity would allow him to assemble new cars from scratch. It would also neatly explain Carlos's missing {{Backstory}}, and the fact he was taking them in place of Worthington would have been the perfect opportunity to mention all this. Marc Brandel, the author of this particular book, also made an effort to include things from earlier in the series, like Jupiter's short-lived career as Baby Fatso, so it seems extremely odd he would not have taken this opportunity to do another ContinuityNod. Instead...this new character Pancho, and we never find out if Carlos and his uncle ended up with a brighter future.
* UnintentionalPeriodPiece: In ''Wandering Cave Man'', the dispute over ownership of the ancient skeleton is between an archaeologist and the white landowner on whose property it was discovered, with no mention of Citrus Grove’s local Native Americans having a claim--very different from modern archaeology under the [[https://en.wikipedia.org/wiki/Native_American_Graves_Protection_and_Repatriation_Act Native American Graves Protection and Repatriation Act]], passed 8 years after the book was published. (Compare the controversy in the book with the somewhat similar dispute over [[https://en.wikipedia.org/wiki/Kennewick_Man Kennewick Man]] in 1996.)
* TheUnTwist: Inverted in ''The Whispering Mummy'' where the character most made out to be ''innocent'' who the boys still suspect (partially due to not being privy to all of the information the audience is) turns out to be innocent.
* ValuesDissonance: Surprisingly and pleasantly avoided for the most part, other than the YellowPeril Mr. Won from ''Green Ghost'' (and not only is his race not emphasized, he's balanced in the plot by the heroic Chang), the uptight and honor-obsessed Mr. Togati from ''Vanishing Treasure'' (who once he discovers he was wrong to dismiss the Investigators fully embraces them and thanks them for their help), and a few disparaging remarks about girls directed at Allie (to be expected from teenage boys). In fact while there are a few examples of old-fashioned views of certain ethnic groups which [[FairForItsDay remain inoffensive]], most of the time such things appear it is to ''disprove'' them, whether outright having such types be proven innocent after being suspected of villainy or having them and their culture actually validated and celebrated; Robert Arthur in particular had a fondness for this, seeing as he shows nothing but sympathy toward the Mexican boy Carlos, the Libyan Hamid, and the Greek Chris, and while he does indulge a bit in [[UsefulNotes/{{Romani}} Roma]] stereotypes in both ''Terror Castle'' and ''Silver Spider'', the first is a case of a movie actor from the silent film era who was deliberately invoking such things to scare the boys and the latter is forced to help by the villain and actually provides the keys to solving the mystery and saving the day. ''Talking Skull'' is even more about averting such views since the Roma are the heroes of the plot. William Arden follows the same path with the Yaquali of ''Laughing Shadow'', carnies in ''Crooked Cat'', and to some degree the Chinese in ''Dancing Devil'', as does M.V. Carey with Wiccans in ''Magic Circle''. However, much is made of the Mexican-American Alvaros' [[HonorBeforeReason pride]] in ''Headless Horse'', and the [[HistoricalHeroUpgrade valorization]] of Cortes in the text is...rather uncomfortable.
** ''Skeleton Island'' has a whole subplot with Chris Markos facing anti-immigrant prejudice and the trio opposing the townspeople who think he's a thief because he's a foreigner. Notably, the boys see the whole thing as idiocy from the get-go and reject such views, as does the town sheriff. The fact Arthur included such a plot and placed the reader's sympathies with the foreigner rather made him ahead of his time in a ValuesResonance fashion.
** On a related note, observe how Uncle Titus and Aunt Mathilda offer every assistance they can (including money) to the poverty-stricken Carlos and his uncle in ''Stuttering Parrot'' (as opposed to suggesting such 'parasites' go back to Mexico or commenting on their illegal status), and how when the Norrises are trying to drive the Alvaros out in ''Headless Horse'', and Pico thinks they would have to go back to Mexico, the boys insist this would be wrong and that they are as much Americans as anyone else. Also, when they find out in ''Deadly Double'' that Jupiter got kidnapped helping the Nandans rescue Ian and prevent the native black people from being placed under a cruel, racist regime, Aunt Mathilda and Uncle Titus both pronounce Jupiter did the right thing and they're proud of him.
** There is, however, the unfortunate example of Hoang Van Don, Hector Sebastian's Vietnamese cook. Although his errors in judgment when it comes to [[CordonBleughChef trying out new recipes]], his misunderstanding of American culture and idioms, and his proclivity for learning via PopCulturalOsmosis result in some genuinely funny moments, overall there is a very uncomfortable sense of being made to laugh at the poor foreigner who just doesn't get the culture he's trying so desperately to fit into. The excessive use of AsianSpeekeeEngrish is also quite grating after a while.
* TheWoobie:
** Letitia Radford of ''Sinister Scarecrow''. While she can be a bit annoying with her strident hysteria, she clearly is a harmless and mostly kind woman. Jupiter obviously has sympathy for her when he notices how haggard and upset she is, remembers Woolley telling them of all the broken engagements she's suffered, and observes that she is no longer young, but instead isolated and lonely. On top of that she has everyone dismissing her plight as her being crazy, and the {{Gaslighting}} itself is rather cruel, particularly when it's only to keep her from discovering a robbery being planned. The fact one of those responsible turns out to be [[spoiler:someone she's known, trusted, and loved since she was a little girl]] is the heartbreaking icing on the cake; it's actually amazing and a sign of how truly good a person she is that she ends up forgiving the person.
** Eleanor Hess of ''Wandering Cave Man'', who is so badly mistreated by her nasty, mocking aunt and uncle that she is convinced she has no worth, is constantly clumsy and shy, and believes no one could ever love her or help her amount to anything. It's no wonder she [[spoiler:decides to help one of the villains rob the [=McAfees=] and ransom the cave man so she can get the money she needs to escape their abuse]], and it's extremely satisfying seeing her not only [[CallingTheOldManOut stand up to them in the end]], but to get the home she deserves and turn it into a place for other lost, lonely girls to stay and get back on their feet.
** Despite (or even because of) his eventual insanity, it's hard not to feel sorry for [[spoiler:Luther Lomax]] in ''Rogues' Reunion'', [[spoiler:forgotten and ignored by everyone in Hollywood, having lost the chance to direct the adaptation of one of Hector Sebastian's books to a younger director, being forced to kowtow to the smarmy PR man Milton Glass, not even given a car by the studio until he begs for it (and points out it would make the studio look bad if they didn't)...]]. The only real issue working against him, other than his insanity, is his arrogance toward the ''Wee Rogues'' [[spoiler:(saying he hated directing them and making it clear he considered doing the show beneath his abilities)]] and in regards to his supposed great talent.
** Carlos and his sick uncle in ''The Stuttering Parrot'', particularly in the scene where they're forced to give away the money they'd just earned for a refund to a rude unsatisfied customer.
** The Potter in ''Flaming Footprints'' was chased out of his country in a violent revolution and spends decades of his life in seclusion safeguarding the treasures of the royal family only [[AllForNothing to find out that it was unnecessary]] both because the sole surviving royal who he was guarding it for (implied to be a close friend of his) [[spoiler:has been DeadAllAlong]] and the new government he has ample reason to hate is apparently turning out to be better by default.
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