Joe (Tony Musante) and Artie (Martin Sheen) are two deadbeat punks who board a New York City subway train late one night and psychologically terrorize the passengers, who include: two soldiers, Pfc. Phillip Carmatti (Robert Bannard) and Pfc. Felix Teflinger (Beau Bridges), the latter of whom has a broken arm; an African-American couple, Arnold and Joan Robinson (Brock Peters and Ruby Dee); an upper-class couple (Ed McMahon and Diana Van der Vlis) with a child; a recovering alcoholic (Gary Merrill); an elderly couple (Jack Gilford and Thelma Ritter); teenage virgin Alice Keenan (Donna Mills); a middle-aged couple where the wife (Jan Sterling) resents her husband (Mike Kellin) who is a school teacher and wishes he had a higher paying job like many of their friends and an unconscious derelict (Henry Proach). Joe is the more aggressive and sociopathic of the two punks, humiliating and degrading the passengers one by one. Artie is passive, docile, and more of a follower.
After Joe finally terrorizes almost all of the adult train passengers, he is finally challenged when he turns his attention to a young child. Joe gets on his knees and tries to convince the childs parents to allow him to speak to her directly. The mother and father are frantic and afraid. Joe tries to touch the child. The father holds his child close to his chest in a protective grip while trying to hide her from Joes sight. Joe is persistent, causing the desperate parents to keep slapping Joes hands away as he tries to touch the child.
Only then does Pfc. Teflinger engage and directly challenge Joe with Stop! Or Ill put you down!. This is when Joe pulls out his switchblade knife. Teflinger engages the punk in hand-to-hand combat. Despite his broken arm and a stab wound from Joe's knife, Teflinger manages to overpower Joe; subsequently Artie drops his tough-guy facade and cowers when Joe is disarmed and overpowered.
The film ends with the police finally entering the train and without asking any questions about what happened here?, start to arrest the only black man. Passengers cry out Thats not the guy! so the cops instead help the almost dead white hoodlum off the floor and out, while a train conductor picks up and helps the other white hoodlum off the train.
No one bothers to help the wounded heroic Teflinger, except for his scared Army buddy whos only contribution was to finally yell out for the police.
The passengers, still frozen in their seats, are stunned. Only when a sleeping drunk sprawled over the seats, rolls over and falls to the floor, do passengers finally awake and slowly exit the train by stepping over the drunks unconscious body.