A chorus laments the ongoing feud between the houses of Capulet and Montague.
In the grand hall of the Capulet palace, party guests assemble for Juliette’s debut as her cousin Tybalt and her suitor Pâris praise her beauty. Capulet presents his daughter to everyone’s delight. The crowd includes a disguised Roméo, Mercutio, Benvolio, and others associated with the Montagues. Mercutio chides his friend’s melancholy, for Roméo’s romantic pursuit of the fair Rosaline has yielded nothing – she is not at the party. Meanwhile, Juliette’s nurse Gertrude is excited about her charge’s potential marriage, but the young girl will have none of it, preferring a carefree life. The lovelorn Roméo spots Juliette, and not knowing she is a Capulet, immediately falls in love. She returns his affection, but their short-lived bliss is interrupted when it is revealed that the new lovers belong to rival houses. Tybalt has recognized Roméo and promises to avenge this affront to the Capulets’ honor.
The page Stéphano assists Roméo in scaling a wall outside Juliette’s rooms, where Roméo and Juliette soon share a tender moment. Grégorio and other Capulets are heard in the distance, looking for the disruptive Montagues, and Roméo hides in the darkness of the garden. After speaking with Grégorio about the intrusion, Gertrude encourages Juliette to go to bed, but the young girl tarries outside, where the two lovers are soon reunited. Juliette suggests they marry the very next day and Roméo heartily accepts her offer.
In the cell of Frère Laurent, the monk celebrates the couple’s union while Gertrude serves as a witness.
Elsewhere in Verona, Stéphano taunts the Capulets with a song. Mercutio defends the young boy from Grégorio’s blade, but is soon drawn into a disagreement with Tybalt. When a freshly-married Roméo happens upon the scene, Tybalt turns his attention to his enemy, but Roméo merely embraces him as kin. Mercutio draws Tybalt into a duel, and in the ensuing melee, is mortally wounded. Now enraged over the death of his friend, Roméo slays Tybalt and is banished from Verona as a result.
As day breaks, the two lovers awaken after a night of passion. Juliette pardons Roméo for the murder of her cousin, and the two languish in bed, refusing to greet the day. But Roméo must leave, and moments after his departure, Gertrude enters, followed by Capulet and Frère Laurent. Angered by recent events, Juliette’s father demands she marry Pâris immediately. Left alone with Laurent, she tearfully comes to terms with her situation, and the monk offers a cure to end her woes – a special potion that will simulate death. Once placed in the family crypt, she will revive in Roméo’s waiting arms.
Having missed a letter revealing Laurent’s plan, Roméo has heard of Juliette’s “death,” and now inside the family vault, laments over her lifeless body. Wishing to join her in eternity, he empties a phial of poison, but as the toxin takes effect, Juliette begins to wake.