Frank, Joe and Chet go undercover as backup drivers when Mr. Hardy asks for their help in investigating a series of hijackings of trucks from the Ortiz Trucking Company in Boston. Clues lead the boys to being secretly trapped on board a freighter bound for Atlantic Island in the Bahamas, where they make an incredible discovery in a mad scientist's laboratory. The title of the book is rather misleading because, even though the boys are trapped at sea twice during the course of the book, it is never for more than a couple of chapters. Despite this, this was a fairly good book. I've never been a huge fan of the doom-and-gloom, world-domination type plots featured in many of the paperback editions, but this story was fairly interesting and moved along at a good pace. This was a worthwhile read, which I think that most fans of the series, particularly the younger ones, would enjoy.