On the West Side in the summer of 1957, there is tension between the Jets (led by Riff) and the Sharks, led by Bernardo. Lieutenant Schrank and Officer Krupke break up a brawl ("Prologue"), warning both gangs to stop fighting or they will be arrested. Despite the warning, the Jets challenge the Sharks to a rumble for neighborhood control.Riff decides that his best friend, Tony (co-founder of the Jets) should fight ("Jet Song"). He invites him to a dance, but Tony is uninterested and tells Riff that he senses something important will happen ("Something's Coming"). Eventually, Tony agrees to come out of loyalty to Riff.Bernardo's younger sister, Maria, tells her best friend Anita how excited she is about the dance. The gangs and girls refuse to intermingle at the dance ("Dance at the Gym"), despite attempts by a social worker. Tony arrives, he and Maria fall in love, and Bernardo tells him to stay away from her. Riff proposes a war council with Bernardo at Doc's drugstore, and Tony leaves the dance thinking about his new love ("Maria").Anita tells Bernardo that he is overprotective of Maria, and they join the rest of the Sharks on the roof of their apartment building to compare Puerto Rico to the United States ("America"). The Sharks leave, and the girls go to bed.Tony visits Maria on her fire escape, and they reaffirm their love ("Tonight"). The Jets wait for the Sharks outside Doc's drugstore and are visited by Krupke, who warns them not to cause trouble. After he leaves, the Jets lampoon him ("Gee, Officer Krupke!"). The Sharks arrive, and the war council begins. They agree to a showdown the following evening under the highway, with a fistfight between Bernardo and Ice. Tony tells Doc about his love for Maria.The next day at the bridal shop, Maria tells her friends how wonderful it is to be in love ("I Feel Pretty"). After closing, Anita mentions the rumble to Maria. Tony arrives; Anita is shocked, and warns them of the consequences if Bernardo learns about their relationship. Maria tells Tony that she has heard about the rumble, and makes him promise to stop it. Tony gives his word, and he and Maria imagine their wedding ("One Hand, One Heart").The Jets and Sharks prepare for the rumble, Anita prepares for her evening with Bernardo, Tony finishes work at Doc's and Maria awaits her evening with Tony ("Quintet"). The gangs arrive, and the fistfight begins. Tony tries to stop the fight, but Bernardo and the Sharks taunt him. Riff hits Bernardo, and the gang leaders draw their switchblades ("The Rumble"). Tony is restrained by Ice and Tiger; Riff is stabbed by Bernardo, who is horrified. An enraged Tony grabs Riff's knife and kills Bernardo, triggering a melee. Police car spotlights illuminate the scene and everyone but Tony flees. Anybodys (a tomboy who wants to be a Jet) shows up, grabs the knives, and she and Tony flee.Maria is waiting for Tony on the roof of her apartment building when Chino tells her what happened. Tony arrives, and asks her forgiveness before turning himself in to the police. Maria tells him not to, and reaffirms her love ("Somewhere").The Jets reassemble in an alley. Action wants to avenge Riff's death, but Ice tells them how to deal with the police ("Cool"). Anybodys warns them that Chino is after Tony with a gun, and Ice sends the Jets to warn him.Tony and Maria are sleeping when a teary Anita brings Bernardo's jacket. Tony tells Maria to meet him at Doc's store so they can elope. Anita chides Maria for their relationship ("A Boy Like That"), but Maria convinces her to help them elope ("I Have a Love").Schrank questions Maria about the rumble, and has Anita go to Doc's to tell him that she will meet him as soon as possible. The Jets do not believe that she is trying to help Tony, and harass her before she can deliver Maria's message. Anita says that Bernardo was right about them, and tells them that Chino killed Maria to avenge her romance with Tony.Doc throws the Jets out of the drugstore, and, in innocence, delivers Anita's false message to Tony. Tony runs into the street, shouting to Chino to kill him as well. He sees Maria, and they run toward each other; Chino steps out of the shadows and shoots Tony. The Jets, Sharks and Doc find Maria holding Tony, who dies as they reaffirm their love ("Somewhere (Reprise)"). Maria stops the gangs from fighting again, taking the gun from Chino and blaming everyone for Tony, Bernardo, and Riff's deaths before she collapses in tears. She kisses Tony; three Jets pick him up, and two Sharks help.The stunned members of both gangs disperse, leaving Chino to be led away by the police.
Output: Question: Whose knife does Tony kill Bernardo with?, Answer: Riff's