The film is set during World War II and revolves around a fortress in the Carpathian Mountains known as "The Keep". The story centers around a group of people - a Russian military commandant (played by Michael Caine), a German officer (played by Robert De Niro), and a British officer (played by Albert Finney) - who find themselves trapped within the keep. The narrative evolves around their complex interactions, strategic military moves, and personal dynamics while navigating the challenges of war.