"Welcome to the Bureau of Investigation." Detective Alexander Riddle hands over the files on seven unsolved mysteries and asks young readers to solve each case. Each file includes Detective Riddle’s original report from the scene of the crime, along with notes describing possible suspects, and any sketches he may have drawn while on duty. The clues to each case are buried in this information and it is up to the reader to put the pieces together and come up with the final report.

In the "Case of the Circus Footprints," Richard Riley, owner of Riley’s All-Star Circus, reports that the cash box with the day’s earnings has been stolen. The only apparent clue to help find the thief is an odd series of footprints leading to and from the circus ticket box office. Did the ticket taker, Tara Blossom, simply walk off with the money, or is Button the clown somehow involved? Then again, maybe Riley stole the money himself! It is up to the reader to find out just whodunit.

With such files as the "Case of the Edible Evidence" and the "Case of the Morning Monsters," Marvin Miller brings humor and fun to each chapter and encourages readers to analyze details and use their critical thinking skills to help Detective Riddle find the answers he can’t figure out himself.