One exciting event follows another when Frank and Joe Hardy are hired to apprehend the pickpockets who have been plaguing Solo's Super Carnival. When their friends Tony Prito and Biff Hooper exhibit a stuffed whale dug up at a construction project, they all but put the carnival out of business. In this thrilling mystery the young detectives pit their wits against a gang of thieves whose bizarre identification, a three-part whale tattoo, proves to be a nearly insolvable riddle.