Professor Peter Williams is obsessed with USS LIONFISH, a WWII US Navy submarine that was mysteriously and suddenly chained, welded shut, sealed and locked to a pier in 1943. Forced to resign from the Navy as a young man due to his obsession with the case, one evening, years later, he receives a visit from a Navy official. With a top secret research team, Peter is asked to descend into the deep and board the submarine for the first time in seventy years. But, once on board and miles under the ocean, the team become trapped, and as the boat begins to reveal its darkest secrets, the prospect of returning to the surface alive begins to fade...