A Confederate raiding party from Canada commandeers a Lake Erie ferry boat in Put-in-Bay and plans to free 2,000 Confederate prisoners on nearby Johnson Island while a spy schemes to destroy the Union gunboat in Sandusky Bay. The raid is complicated by a seedy French-Canadian, a mysterious trunk and a body found on Rattlesnake Island where rainbows end. One hundred forty plus years later, Emerson Moore, an investigative reporter struggling with the tragic death of his wife and son, returns to visit his aunt in Put-in-Bay where he incurs the animosity of a wealthy shipping magnate who lives in a ship's bow on South Bass Island's west side.

Moore meets an Ohio State University professor who is studying the island's caves and encounters a number of challenges when he falls in love with the professor's married daughter with whom he shares a haunting memory from his boyhood island days and solves the mystery of the missing trunk.