June 1961. The Sovjet leadership is anxious to get its submarine prototype K-19 to sea, in order to test a launch of a nuclear missile. However, Captain Polenin doesn't approve as the prototype ship is not certificated yet to perform such a manouvre. He's being replaced by Captain Vostrikov, who is keen to prove himself a tougher and fearless submarine man. On its way to the test field, Vostrikov makes the nervous crew undergo rigorous test drills and dangerous manouvres, and suddenly the disaster strikes. The reactor cooling system starts to leak, and to avoid a melt down, crew members must expose themselves to radiation in order to keep control over the reactor.
Based on actual events kept secret until recently, bearing the Kursk tragedy in mind, this is a frightening tale of incompetance on many levels.