In summer 1957 in the West Side’s Lincoln Square neighborhood in Manhattan, there is tension between a white American gang, the Jets, led by Riff, and a Puerto Rican gang, the Sharks, led by Bernardo. After a brawl erupts, Lieutenant Schrank and Officer Krupke arrive and break it up. The Jets decide to challenge the Sharks to a rumble at an upcoming dance for neighborhood control.
Riff decides that his best friend Tony, the co-founder of the Jets who left the gang, should fight. Riff invites Tony to the dance, but Tony is uninterested. He tells Riff that he senses something important will happen, which Riff suggests could have a correlation with the dance. After a little more persuasion, Tony reluctantly agrees to go.
Bernardo’s younger sister, Maria, tells her best friend and Bernardo’s girlfriend, Anita, how excited she is about the dance. At the dance, the gangs and girls refuse to intermingle. Tony arrives and he and Maria fall in love. However, Bernardo angrily demands that Tony stay away from her. Riff proposes a meeting with Bernardo at Doc’s drug store at midnight.
Maria is sent home; Anita argues that Bernardo is overprotective of Maria and they compare the advantages of Puerto Rico and the United States.
Tony discreetly visits Maria on her fire escape, where they reaffirm their love. Krupke, who suspects the Jets are planning something, visits them and warns them not to cause trouble. When the Sharks arrive, both groups agree to have the showdown the following evening under the highway, with a one-on-one fist fight. When Schrank arrives, the gangs feign friendship. Schrank orders the Sharks out and unsuccessfully tries to discover information about the fight.
The next day at the bridal shop, Anita accidentally tells Maria about the rumble. Tony arrives to see Maria, which shocks Anita. They profess their love and Anita warns them about the consequences if Bernardo learns of their relationship. Maria has Tony promise to prevent the rumble. Tony and Maria fantasize about their wedding ceremony.
The Jets and Sharks approach the area under the highway. Tony arrives to stop the fight, but Bernardo antagonizes him. Unwilling to watch Tony be humiliated, Riff initiates a knife fight. Tony tries to intervene, which leads to Bernardo killing Riff. Tony kills Bernardo with Riff’s knife and a melee ensues. Police sirens blare and everyone flees, leaving behind the dead bodies.
Maria waits for Tony on the rooftop of her apartment building when her fiancé Chino arrives and tells her what happened. Tony arrives and explains what transpired and asks for her forgiveness before he turns himself in to the police. Maria confirms her love for him and asks Tony to stay with her.
The Jets have reassembled outside a garage, with their new leader, Ice, having them focus on reacting to the police. Anybodys arrives and warns them that Chino is now after Tony. Ice sends the Jets to warn Tony.
Anita enters the apartment while Tony and Maria are in the bedroom. Tony and Maria arrange to meet at Doc’s, where they will pick up getaway money to elope. Anita spots Tony leaving through the window and chides Maria for the relationship, but Maria convinces her to help them elope.
Schrank arrives and questions Maria about the rumble. To cover for Tony, Maria has Anita tell him that Maria is detained from meeting him. When Anita reaches Doc’s, the Jets harass her, until Doc intervenes. Anita declares that Bernardo was right about them and that Chino killed Maria. Doc banishes the Jets and gives Tony his getaway money in the basement and delivers Anita’s message. Tony runs into the streets, shouting for Chino to kill him as well.
In the playground next to Doc’s, Tony spots Maria and they run toward each other, only for Chino to shoot Tony. The Jets and Sharks arrive to find Maria holding Tony, who dies in her arms. Maria stops the gangs from fighting, takes the gun from Chino and threatens to shoot everyone, blaming their hate for the deaths. Schrank, Krupke and Doc arrive and the gangs form a funeral procession, with Maria following. The police arrest Chino and lead him away.