A terrorist attack disables a US Navy submarine in dangerously deep waters off the coast of Florida. The Navy is compelled to use its least-favorite strategy to complete a rescue of the submarine crew: send divers to extreme depths. Can a team of the Navy's best ultra-deep divers perform this mission? When things go perilously wrong, can a novel approach in diving physiology that has not been fully tested under controlled laboratory conditions save the rescuers? The plot twists back and forth in time between calm and happy days of friends working together in the laboratory and the drama of the rescue mission.