A bitter tension between the jets, a self-styled “American” street gang, and the Sharks, a group of young Puerto Ricans opens the scene. The leader of the jets, Riff swears to drive the Sharks, led by Bernardo, from the streets. Riff determines to challenge Bernardo that night at a dance in the gym, and prevails upon his old friend and the co-founder of the Jets, Tony, to help him. Tony has been growing away from the gang, and feels the stirrings of other emotions but reluctantly agrees.
Bernardo’s sister Maria, newly arrived from Puerto Rico to marry his friend Chino, attends the dance and despite the obvious hatred between the gangs meets Tony, who at once falls in love with her. Later, after the dance, while the gangs begin to assemble at Doc’s drugstore to choose a place and weapons for their rumble, Tony visits Maria on the fire escape of her apartment, and they pledge their love, promising to meet the next afternoon at the bridal shop where Maria works. As he departs, the Sharks take their girls home and go off to the drugstore, while a playful argument develops between Anita and homesick Puerto Rican girls over the relative merits of life back home in Manhattan.
At the drugstore, the Jets are edgy about the approaching meeting with the Sharks, but Riff advises them to play it cool, and when the Sharks arrive, an agreement is reached, at Tony’ s insistence, to have a fair, bare-handed fight between the best two fighters in each gang. The following day, Tony visits Maria at the shop and among the clothing dummies they enact a touching wedding ceremony. Maria makes him a promise to stop the fight between his gang and his brother’s. in the quintet Tonight, Tony and Maria sing for their love, Anita makes plans for a big evening, and Bernardo and Riff and their gangs make their own plans for rumble.
In a deserted area under the highway, gangs meet for the fight. As it is about to get underway, Tony hurries in, and begs them to stop, as he is promise to Maria. Bernardo enraged that Tony has been making advances to his sister, pushes him back furiously. Suddenly switch-blade knives appear, and Riff and Bernardo begin to fight. In the ensuing action, Riffed is knifed, and Tony, grabbing his own weapon, in turn knifes Bernardo. Frenzied, the gangs join battle, until they are interrupted by a police whistle. They flee, leaving behind the bodies of Riff and Bernardo.
In her room, Maria is gaily preparing for her meeting with Tony. She is unaware of what has happened, until Chino bursts into her room and tells her that her brother has been killed by her lover. Seizing a gun, he rushes out in search for Tony. Tony, however, has climbed the fire escape to Mari’s room, and in spite of her grief she is unable to send him away. Clinging together desperately they envision a place where they can be free from prejudice. In the streets and alleys the gangs flee the police, panic-stricken by the killings. Two of the Jets, Action and Snow boy, have already been questioned, and they explain to the rest of them how to handle the adults.
The sorrowing Anita knock’s at Maria’s door, and Tony leaves by the window, taking refuge in the basement of Doc’s drugstore. Anita upbraids Maria for allowing Tony to come near her, but Maria’s answer carries it’s certain force, and a length Anita agrees to go warn Tony that Chino ginning for him. She goes to the drugstore, but is brutally taunted by the Jets for her nationality, and finally in hysteria spits out a different message for Tony: that Chino has killed Maria revenged. Doc tells Tony what Anita has said, and Tony leaves his hiding place, wandering numbly on the streets. At midnight, he runs to Maria, who has been searching for him, but their moment is brief: Chino appears from the shadows and, drawn together by the tragedy, lift up the body of Tony and carry it off.
* Riff-quick-tempered but zany leader of the Jets.