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.

The sewer system has three types of sewer tunnels. Tunnels with solid dry floors, tunnels with a water passage in the middle and tunnels with pits. Sam can walk, run and creep through the tunnels but Sam can't move as quickly in water. Sam can move from tunnel to tunnel by entering one of the passages that appear occasionally on his way. Each time he enters a new sewer, Sam receives a fresh supply of oxygen.