The Secret of Terror Castle, the first T3I novel, written by Robert Arthur in 1964.
It begins with the actual founding of The Three Investigators team, with the printing of the first business cards. It isn't uninteresting to see the HQ already being around, as it used to be just a meeting point used by Jupe, Pete, and Bob for solving minor mysteries and now becoming THE place for them to found a detective team.
Jupe uses his talent as an actor (which he gained as a child actor, a time he obviously isn't proud of) to get to Alfred Hitchcock in order to look out for a haunted castle for him. Given how he won a lottery using his mathematic and logical gifts, he won a Rolls-Royce including a driver called Worthington, coming from the UK. Passing by is even more obstacled due to Henrietta Larson, who happens to be T3I's former schoolmate and now serves as Hitchcock's secretary. Well, for a given definition of the term "school-MATE", as one should say, given her nickname "Bossy Henrietta" for reasons.
Imitating Hitchcock's posh British accent was probably not that impressive.
But Jupe was able to convince Hitchcock. Bob, disabled due to an accident, managed to find a haunted castle.
In a series of accidents (the most prominent being one attributed to their arch-rival E. Skinner Norris by finding his flashlight saying "E.S.N." - but that, as Pete says, could also be for "Exceptionally Scared and Nervous") and ways to scare T3I in a way which was obviously new to common scientific knowledge in the 1960s, T3I manage to solve the mystery about a former actor from the 1920s, whose voice didn't match the audience's expectations afterwards, given how pitched it was.
And let's not forget the part Jupe making his legs do what he wants. To run.
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"The Secret of Terror Castle" was the beginning of an era. For me, it's a pity, that the series gave its initial run in the 1960s and ended within the very same decade, from Arthur's perspective. If he could have had more knowledge as to how "The Secret of Terror Castle" has been adopted into audio dramas in Germany specifically and also in the UK, what could HIS OWN inscenation have been like, had he been given more years to live? Given that his career as an author of audio dramas himself, I personally wouldn't call it unlikely to assume, that in case he had lived a few years more, we could have audio dramas of T3I as well. The ways he created his style of writing, clearly focussed on dialogues, which shows the quality of his writing the most, might make this obvious, or at least assumable. Sadly, this is for a better world to know ...
But of course, this issue leads too far and should be discussed somewhere else. By the way, may I adopt the phrase "to shudder positively" into my vocabulary, just in case I'll ever end up in a need of it? It sounds as if it wants to give somehope a small bite of hope. 