When the disappearance of the Boys' chums, Chet and Biff, occurs, they take a motorboat trip down the coast. When Frank and Joe find them, they were all captured. In the end, they win over the bad guys on mysterious Blacksnake Island. At the beginning of the book the boys take their new boat, the Sleuth, out on the bay. While they are cruising on the bay another boat nearly rams them. They would have chased the boat but the steering on the Sleuth broke! How will the Hardy Boys rescue their friends and close this case?