The film stars Tony Musante and Martin Sheen (in his first film role) as two street hoods who terrorize 14 passengers sharing a New York City Subway car, played by an ensemble cast that includes Beau Bridges, Ruby Dee, Jack Gilford, Ed McMahon, Gary Merrill, Donna Mills, Brock Peters, Thelma Ritter, and Jan Sterling.
After giving a hard time to a pool hall owner for closing early, they briefly harass a passing couple, then mug an old man for his eight dollars and beat him into unconsciousness.
At the Burnside Avenue station, after leaving a cocktail party, middle-aged Muriel Purvis boards with her mousey husband, Harry, whom she resents for earning less money than many of their friends and having no ambition; at 176th Street, out-of-work, recovering alcoholic Douglas McCann, boards, joined by Kenneth Otis, a homosexual who earlier made an unsuccessful attempt at befriending McCann.
Eden Avenue, frustrated and angry Arnold Robinson, and his long-suffering wife Joan, a black couple, board after attending a charitable event for inner-city youth.
They start with the derelict to whom they attempt to give a hot foot, then move to Douglas, then to Kenneth – whom they physically prevent from leaving the train – and so on.
When the train crosses into Manhattan, the Robinsons' 125th Street station comes up first, but Arnold, enjoying the spectacle of white people tormenting each other, makes Joan stay with him to watch.
Carmatti shouts into the station for the police, who enter the train and, without asking any questions, start to arrest the only black man in the car, Arnold.
In order to get the necessary footage, cinematographer Gerald Hirschfeld and his son rode the subway and surreptitiously shot the moving background with a camera hidden in a cardboard box.
[citation needed] Hirschfeld said in an interview that he filmed in black and white in order to get "the most realistic style of photography possible"; test shots were taken in muted color, but they were deemed a distraction from the desired "somber" effect.