The Sharks and the Jets conduct a "war-council" session in the store, peppered with insults and derogatory epithets:

Riff: We challenge you to a rumble. All out, once and for all. Accept?
Bernardo: On what terms?
Riff: Whatever terms you're callin'? You crossed the line once too often.
Bernardo: You started it.
Riff: Who jumped Baby John this afternoon?
Bernardo: Who jumped me the first day I moved here?
Action: Who asked you to move here?

The Sharks accept the rumble, planned for the next day "after dark" under the highway. Tony enters the store as they are discussing the call for weapons, with increased tempo and volume: "Rocks, belts, pipes, cans, bricks, bats, clubs, chains..." He interrupts the cadence between the two sides:

Tony: Bottles, knives, guns. What a coop full of chickens?
Action: Who are you calling chicken?
Bernardo: Every dog knows his own.
Tony: I'm calling you all chicken. Big tough buddy-boys gotta throw bricks, huh? Afraid you're getting close? Afraid to slug it out? Afraid to use plain skin?

Now "in love," Tony suggests a rumble that is also a "fair fight if you've got the guts to risk that? Best man from each gang will slug it out." He persuades them to accept a fist fight between the strongest representatives from each side for a decisive, final battle. Bernardo threatens Tony personally, thinking that he will be selected as the representative: "When I get through with you, you will be like a fish after skinning."

The prejudiced Lt. Schrank intrudes and is amazed to find the members of the gangs peacefully socializing together in Doc's place. He accepts credit for the relaxation of tensions - although it is a sham - and then viciously throws the Puerto Ricans out:

I get a promotion and you Puerto Ricans get what you've been itchin' for. Use of the playground, use of the gym, the streets, the candy store. So what if they do turn this whole town into a stinkin' pigsty. (Bernardo bursts up from his chair, and is restrained by Riff) Don't stop him. He wants to get home. Write a few letters to San Juan, tell them about how he's got it made over here. What I mean is, CLEAR OUT! I said CLEAR OUT. (Seething with restrained anger, Bernardo stares at Schrank from a few feet away) Oh yeah, sure, I know. It's a free country and I ain't got the right. But I got a badge. Whaddya you got? Things are tough all over. BEAT IT!

The Sharks exit, whistling "My Country Tis of Thee" as they depart.

Claiming that he's for them, Schrank wants the Jets to divulge where the rumble will be held: "I want this beat cleaned up and you can do it for me. I'll even lend a hand if things get rough. Now, where are ya gonna rumble?" He chastises them when no one answers with foul-mouthed insults: "Why don't you get smart, you stupid hooligans? I oughta take you down to the station and throw you in the can right now. You and the tin-horn immigrant scum you come from." As they leave, he threatens to be there at the rumble: "Don't worry. I'll find out where it's gonna be. So be sure to finish each other off because if you don't, I will."

In the bridal shop the following day, Maria models fancy hats, coyly agreeing that she is "crazy" in love, "looks somehow different," and "is up to something." She tells her gossipy Puerto Rican girlfriends "what is going on" by singing "I Feel Pretty":

I Feel Pretty:

(Maria) I feel pretty, oh so pretty, I feel pretty and witty and gay,
And I pity, any girl who isn't me today
I feel charming, oh so charming, it's alarming how charming I feel
And so pretty, that I hardly can believe I'm real
See the pretty girl in that mirror there? Who can that attractive girl be?
Such a pretty face, such a pretty dress, such a pretty smile, such a pretty me!
I feel stunning and entrancing, feel like running and dancing for joy
For I'm loved by a pretty wonderful boy
(Girls) Have you met my good friend Maria, the craziest girl on the block?
You'll know her the minute you see her, she's the one who is in an advanced state of shock
She thinks she's in love, she thinks she's in Spain
She isn't in love, she's merely insane
It must be the heat or some rare disease
Or too much to eat or maybe it's fleas
Keep away from her, send for Chino
This is not the Maria we know
Modest and pure, polite and refined
Well-bred and mature and out of her mind
Miss America, Miss America, speech!
Miss America, bravo, speech!
(Maria) I feel pretty, oh so pretty, that the city should give me its key
A committee should be organized to honor me
I feel dizzy, I feel sunny, I feel fizzy and funny and fine
And so pretty Miss America can just resign
(Maria and Girls) See that pretty girl in that mirror there, (What mirror, where?)
Who can that attractive girl be? (Which, what, where, whom?)
Such a pretty face, such a pretty dress, such a pretty smile, such a pretty me!
I feel stunning and entrancing, feel like running and dancing for joy
For I'm loved by a pretty wonderful boy

Since it is six-o'clock and quitting time, Maria tells Anita that she will be locking up the shop: "I have work." After taking a luxurious bubble bath with Black Orchid, Anita is expecting a date with Bernardo following the evening's rumble between the Sharks and the Jets. Peace-loving Maria doesn't understand the politics of gang warfare:

Maria: What rumble?
Anita: Oh, well, uh, 'Nardo's Sharks and those boys at the dance.
Maria: They fight each other tonight?
Anita: They don't play patsy.
Maria: Why must they always fight?
Anita: Well, you saw how they dance, like they got to get rid of something quick. That's how they fight.
Maria: To get rid of what?
Anita: Too much feeling, and they do get rid of it. Boy, after a fight, that brother of yours is so healthy.

Tony arrives to see Maria - Anita gives both of them a knowing look and a sarcastic rendering of Maria's self-less helpfulness: "I will lock up." She gives them a worried look and warns them about defying loyalties and breaking the rules of their respective societies: "You're out of your heads." Maria urges Tony to go to the rumble as a peacemaker, to stop the fist fight between Bernardo and Ice:

Maria: You must go and stop it.
Tony: I have stopped it. It's only gonna be a fist fight now between two of 'em...
Maria: Any fight is no good for us.
Tony: Maria, everything is good for us. We got magic.
Maria: Listen and hear me. You must go and stop it.
Tony: It means that much to you?
Maria: Yes.
Tony: All right, I will then.
Maria: I believe you. You do have magic.
Tony: Of course, I've got you.

They playfully pantomime their engagement and wedding with mannequins that represent the in-laws and other members of their families. With a bridal veil on her head, and a black top hat on his head, they walk down an imaginary aisle in the store and enact their wedding. As a couple, they kneel and exchange marital vows. The setting resembles a church and an altar - the store's window above them with a cross bathed in gold light accentuates the holy nature of their bonding: "'til death do us part." Their soothing duet, "One Hand, One Heart," establishes their oneness as they exchange private vows:

One Hand, One Heart:

(Tony) Make of our hands one hand, Make of our hearts one heart
Make of our vows one last vow, Only death will part us now
(Maria) Make of our lives one life, Day after day one life
(Tony and Maria) Now it begins, now we start
One hand, one heart, even death won't part us now

The scene abruptly changes to a blood-red sky, and the approach of the combatants, Sharks and Jets, toward their eventual confrontation at the rumble, sung by all gang members. Verses and cross-cut scenes in the same dance and song sequence "Quintet" show paralleling, interwoven events from the perspectives of different characters (the gangs, Anita, Tony, and Maria) as they each face the night. Anita expects to get her kicks in a "private little mix" with her "hot and tired poor dear" Bernardo. Tony sings: "I'll see my love tonight and for us stars will stop where they are." Maria is impatient with the slow passage of time:

Today the minutes seem like hours, the hours go so slowly and still the sky is light. Oh moon, grow bright and make this endless day endless night.

The Puerto Ricans scale a tall chain-link fence under the highway. The Jets appear on the top of a facing concrete wall, jump down, and face them. After dispensing with the shaking of hands, Bernardo urges: "Look, every one of you hates every one of us, and we hate you right back. Let's get at it." Tony interrupts the rumble, the hand-fight between Ice and Bernardo, after it has just begun: "Hold it!" He steps between the two gang combatants to mediate and prevent senseless fighting. The leader of the Jets challenges and taunts Tony to fight in a warm-up bout: "Afraid pretty boy? Afraid gutless? Afraid chicken?...You yellow-bellied chicken...Pollack."

During the elaborately-choreographed, action-oriented dance/fight, Riff defends Tony and punches Bernardo - the two pull out gleaming switchblades and escalate the conflict to deadly proportions. Riff is disarmed and stands defenseless in front of a chain-link fence, but is given another blade by a fellow gang member. Meanwhile, Tony is held back by the Sharks. Bernardo accidentally kills Riff with a single plunge of the knife to his mid-section. As he falls, Riff passes his switchblade to Tony. In retaliation to counter Riff's death, Tony vengefully and passionately stabs and kills Bernardo. The sounds of police sirens force the gangs to scatter. Two bodies are left at the scene. Despite his intentions, he has caused further bloodshed. Horrified and anguished, Tony cries out: "Maria!" A spotlight catches Tony in its circular beam, pronouncing him guilty in the tragedy. A church bell tolls the time - a somber death knell.