this was about 3 boys one i think was called jupiter they had a caravan as an office in jupiters uncles junk yard the most famous one was called terror castle books by alfred hitchcock
Detectives - Juvenile detectives - this book series was first with the rather impressive title of "Alfred Hitchcock and the Three Investigators."
However, it didn't actually have anything to do with Alfred Hitchcock - his name was simply on the product as the initial writer - Robert Arthur - was an editor on some Hitchcock book collections.
Most of the mysteries were of the type of twilight zone or outer limits and involved investigation of strange and baffling phenomena like an ancient Egyptian mummy that talked or a talking human skull.
Great fun, and