In 1991, acting on a tip from a local fisherman, two scuba divers discovered a sunken German U-boat - complete with its crew of 60 men - not too far off the New Jersey coast. The divers, realizing the momentousness of their discovery, began probing the mystery. Over the next six years, they became expert and well-traveled researchers, taught themselves German, hunted for clues in Germany, and constructed theories corrective of the history books, all in an effort to identify this sunken U-boat and its crew. During that time, three of their colleagues died exploring the wreck, including a father and son team. In 1997, when it all seemed in vain, the two divers came up with a final plan, so dangerous that the book ends with this last dive.