Cold War submarine crews from both the Soviet and American navies describe missions few outsiders ever heard about, in interviews shot decades after they left the service. The K-19 accident anchors much of the film: one of the Soviet Union's first nuclear-armed submarines, rushed into service, suffers a cooling system failure in its reactor, and sailors describe the men who worked inside the reactor compartment to fix it, absorbing radiation doses that left them with burned skin, damaged vocal cords, and days to live. The K-129 supplies the film's unsolved case, a Soviet sub destroyed in 1968 under circumstances still debated, possibly during preparations to fire on Hawaii, followed by a covert American salvage attempt six years later that only partly succeeded. Alongside these, the film gives an inside look at the NR-1, a small American research submarine built for espionage work. Testimony carries the narrative throughout, from men who served in cramped, dangerous conditions where a single malfunction could be fatal.