K-219 performs a Crazy Ivan, and USS Aurora collides with her, causing a rupture of the seal on one of its ballistic missile tubes. The leaking seawater causes a corrosive reaction which floods the sub with toxic gas. The corrosive reaction starts a fire that floods the sub with more toxic gas, and smoke. The captain surfaces the boat and moves the crew out to the deck, and attempts to vent the sub. The chief engineer informs the captain that the fire may cook off the nukes and cause a nuclear explosion. The launch doors are opened on the sub to vent smoke. Aurora ascertains that a fire is aboard K-219, and informs the Pentagon. The Pentagon, fearing radiological contamination of the Eastern Seaboard, orders Aurora to prepare to sink K-219. The fact that the launch doors are open on the SLBMs causes consternation in Washington D.C., with calls for the immediate sinking of the sub, should it appear to be preparing to launch. The captain of K-219 prepares a bold plan to dive with the launch doors open, to flood the missile bay and quench the fires. As the captain dives the sub, Aurora prepares to fire, assuming K-219 is setting about to launch its missiles. After a brief but heated argument the U.S. commander is convinced to wait before launching and realises that the Soviet sub is diving, rather than launching its SLBMs. K-219's tactic works, and the sub resurfaces with the fires out. A new crisis develops: Both nuclear reactors are overheating, and the cooling rods must be lowered manually by two crew members who have only limited oxygen left. The rods are lowered, and both reactors are shut down, averting disaster, but one crew member remains locked inside the reactor room, running out of oxygen. With seawater flooding the submarine, the captain of K-219 decides to abandon ship. Throughout the crisis, Washington insists that no information on the possibility of nuclear fallout along the eastern American coastline be leaked to the Governors and no evacuation plans be activated to protect the population, in order not to derail the forthcoming Reykjavik Summit between Soviet leaderMikhail Gorbachev and U.S. President Ronald Reagan. Capt. Britanov and his surviving crew members return safely to Moscow with some crew decorated and he being dismissed from the navy. The Reykjavik Summit takes place as planned. The film's postscript details that as a legacy almost a decade after the end of the Cold War, fifty one nuclear war heads and seven nuclear reactors from nuclear submarines litter the North Atlantic ocean floor.
