It's a lovely day and Sam is waiting in Central Park to meet his girlfriend Sally. He sees her and walks to her. He only has eyes for her and before he realizes it he finds himself in the New York sewer system.
Three Russian submarines have been located in the New York sewer system and they have blocked off the system. Sam's only way out of the sewer system is to destroy the Russian submarines. Luckily, Sam carries his revolver. Sam can't go back... once he's gone through the City Sewer Department seals the tunnel. Luckily, Sam carries his revolver.