These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Foe Yay: A bit disturbingly, Huganay towards Jupiter in "The Mystery of the Screaming Clock." As the book was originally published in the late 60's, at least part of it is due to changing standards of what is viewed as appropriate behavior towards a young teenage boy, and it seems as though the writers were merely aiming to characterize Huganay as Affably Evil. Nevertheless, Huganay, described as "dapper" and "debonair," always seem to be "whispering into Jupiter's ear," and "wrapping his powerful arms" around Jupiter to hold him still and putting a hand over his mouth to stop Jupiter from yelling for help. He alternately speaks "softly" and "mockingly" to Jupiter, whilst seeming to relish in the advantage he gains over him.
He's quite flattering toward Jupiter, as if he's deliberately trying to be charming, addresses Jupiter with various fond epithets such as, "my boy," and "my plump but clever young friend." He also places a hand "earnestly" on Jupiter's shoulder and tells him, "I like spirit in a boy," while assuring Jupiter that their teamwork would be brilliant if they were to work together. Additionally, Huganay bestows Jupiter with various compliments, referring to the Three Investigators, (which he knows was Jupiter's creation) as "an ingenious organization," and telling Jupiter, "Your mind hums like a top."
Considering Jupiter is somewhere between the ages of 13-15 and Huganay is an elite adult criminal whose sincerity is doubtful, it can be slightly uncomfortable.
Genius Bonus: 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 Harold Thomas in Magic Circle, is how Jupiter identifies him as 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 Serial Numbers Filed Off); the history of Fremont's expedition in California during the Mexican War in Headless Horse; and the bit with Indonesia once having been a Dutch colony being how Harold Thomas, who ate at an Indonesian restaurant, was revealed as Charles Goodfellow, original native of Holland, in Magic Circle.
Germans Love David Hasselhoff: 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 Audio Adaptation of The Three Investigators. The voice actors of the three heroes (who were never 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 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.
Somewhat related to Germans Love David Hasselhoff since the Audio Adaptation of the Three Investigators is hugely popular in its own right, arguably even more so than the actual books. Due to its long running time (well over 30 years) the voice actors have developed sort of their own spin on the titular investigators and over the years it has deviated quite a bit from the original source material. All the while influence from the show started creeping into the newer books too, largely because the young authors of said books grew up with the show that is in turn based on the books they're now writing. Confused yet? So what does all this have to do with Ho Yay? Simple. These are the two voice actors of Peter and Bob, in a live stage audio adaptation, of the Three Investigators in character. This is the tame version to boot—there is an outtake where 'Bob' outright dipped 'Peter' in a very passionate kiss and full body embrace. To put it in Andreas Fröhlich aka Bob's words : "I think Jens (Peter) finally expected tongue action that night." Cue curious editor asking if he (Jens) got it. No. But he did imply that he groped him.
To the point that whenever Jeffery is mentioned in newer episodes, Bob gets extremely jealous of him much like a boyfriend jealous of someone's ex.
Also the show tended to shift lines from Kelly to Bob even before she left the show, leading to a moment where Bob is pretty much having a mini meltdown about his 'friend' note In German boyfriend and friend is covered by the same word and it becomes clear from the context which one is meant mostly, making this one very ambiguous. being missing, while Kelly calmly sat by not concerned in the least...
As of Episode 163 we have an 'on screen' kiss between the two after Peter solves the puzzle of the day, which was led up to by this exchange:
Peter : ...get it?
Bob : (excited)OF COURSE! Oh Pete, I could kiss you!
Peter : (embarrassed) Ehrm....not...not here... (They go on explaining the puzzle)
Jupiter: You solved it, Second!
Bob : (slightly breathy) Can I kiss you now?
Peter : Go ahead! *cue smoochie sounds*
Magnificent Bastard: Hugenay, at least in Screaming Clock. He pursues Bob and Harry to steal the clock, then disappears just in time for the cops to take them in for speeding, then has the audacity to steal it from their car while they're in the station. He slips a tracking device in Jupiter's coat pocket just before he goes to join Carlos, Gerry, and Jeeters so that, even when they lose him in traffic, he's able to find where they are and break in—with cops to arrest them. Except they're actually his own men merely dressed as cops. And then at the climax, when it seems he's about to escape with the missing paintings, the real police show up...only because the paintings have been found without being stolen, all the damage done to the house was with Harry's mother's permission, and even the "cops" can't be charged with impersonating the LAPD because their uniforms are mere Halloween costumes (and of NYPD officers), he can't be arrested for anything and walks off scot-free.
The Scrappy: Allie Jamison could be considered this, particularly in Death Trap Mine. The fact she turned out to be right about Thurgood in the end (albeit not at all in the way she thought, and nothing to do with the main case they were investigating) didn't stop her smug attitude and Single-Issue Wonk from becoming irritating. May even have been invoked in-story when Jupiter says something deliberately geared to upset her just to get her to leave.
At least in the newer German releases, the boys do consider her to be this until much later on.
They Changed It, Now It Sucks: 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.
Values Dissonance: Surprisingly and pleasantly avoided for the most part, other than the Yellow Peril 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 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 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 gypsies are the heroes of the plot. William Arden follows the same path with the Yaquali of Laughing Shadow, carnies in Crooked Cat, and the Chinese in Dancing Devil, as does M.V. Carey with Wiccans in Magic Circle. However, much is made of the Mexican-American Alvaros' pride in Headless Horse, and the valorization of Cortes in the text is...rather uncomfortable.