From the publisher:
The purchase of a houseboat for a customer at Mr. Hollister's sport and toy store, The Trading Post, sends the Hollister family to Circus Island, the home of the Sunshine Circus, in Florida. Before they are to leave, however, Pam enters her dog Zip in a dog show where the theft of two French poodles and an injury to Zip begin a mystery which has some connection with the Hollisters' destination in Florida. The five Hollister children are amazed when they discover the thief at the dog show has preceded them all along the way to Circus Island. Through clues, such as a handbill announcing the Wizard Circus and the disappearance of another dog, they learn the thief's activities are far more sinister than anyone had at first suspected. Along with the strange occurrences of the mystery is the inside story of a circus. The boys learn a tumbling act, Holly tries her skill at tightrope walking, and they all find that a clown's smile is sometimes only a happy mask that hides sorrow.
