While fishing one day in his small rowboat, William Constable caught a glimpse of something unusual in the water. The almost-eleven-year-old lost his balance and fell into the water. So begins this tale about a lovable sea monster named Chessie, who lives in Heron Creek. Soon after his mishap, William introduces Tommy to Chessie, and every day the boys row down the creek to play with her. But a cruel, greedy man sees their secret pet and plots to trap her. The nigh-time rescue operation that William and Tommy undertake will thrill readers young and old.