The film tells the story of the tragic end of the Kursk, the flagship of Russian nuclear submarines and the death of its 140-member crew.
While the Kursk participates in a naval exercise in the Barents Sea, a pressure build-up in the torpedo tubes causes one of the torpedoes to explode. The front part of the Kursk is destroyed and the submarine uncontrollably sinks to the bottom of the sea. Miraculously, a small group of sailors manages to hide in the last compartment at the back of the submarine. In all, eight men with Dimitri Kolesnikov as their leader, try and survive in the compartment progressively filling up with water, hoping the Russian navy will save them.
Even if the attempts by the Russian government to save the crew are failing due to insufficient technology, the Russian military authorities refuse to accept help from the American, British and Norwegian navies.
For the survivors and their families, wavering between fatalism and revolt, a race against the clock starts, while the Russian authorities hesitate to choose between national pride and the lives of their compatriots.