The three detectives are his young friends Bob Andrews, Pete Crenshaw and Jupiter Jones. They live in a town near Hollywood. Their stronghold is a salvage warehouse, their headquarters is an old caravan in which they have equipped a crime laboratory. Their agency "Three Detectives" reveals any secrets, riddles and puzzles. Friends-detectives boldly take on the most important and complicated cases and bring them to the end with honor.

The Mystery of the Valley of Moans While relaxing on a ranch with friends of the Yupa family, the guys encounter strange moans coming from a nearby cave. Is it the moaning ghost of an elusive robber nicknamed the Devil or is it just the wind walking through the underground labyrinths?

The book contains illustrations.