For most of her crew, HMS Retaliate's Baltic cruise in 1960s is a routine one, and her sixteen nuclear missiles no more than a silent threat to the Russians. But the submarine's captain, Commander Shadde, is obsessed with the communist menace and haunted by the memory of his one act of cowardice. As the submarine approaches the end of her voyage, a letter from his wife threatening divorce pushes Shadde to the brink of madness in a vessel where nuclear war is just a button away…