Tonio announces that the author wanted to revive the traditional customs of the commedia dell’arte, but the difference is that they are trying to show ‘a slice of life’, and the people you see onstage are flesh and blood.
Crowds welcome a troupe of actors arriving to town. Canio, the head of the troupe, invites everyone to come to their show at 11 that evening. Canio and Beppe head to the tavern for a drink, leaving Tonio alone with Nedda, Canio’s wife. She muses on the fierceness of his jealousy and dreams of her freedom. Not until her song is finished does she notice Tonio watching her. Clumsily he tries to declare his love for her, but she mocks him. When he tries to kiss her, she hits him. Screaming revenge, Tonio leaves her as Silvio, Nedda’s lover, appears. As they talk lovingly, Tonio sneaks in and overhears Nedda and Silvio’s plan to elope that night after the show. Tonio goes to fetch Canio.
When Canio returns, he threatens Nedda to reveal to him her lover’s name, but she refuses and Beppe has to restrain Canio, reminding him they have a show to perform. Left alone, Canio muses bitterly about the hard life of the clown who has to hide his pain behind his makeup.
The audience arrives, and the play begins. Harlequin (Beppe) serenades his beloved Colombina (Nedda), who knows that her husband Pagliaccio (Canio) will not return home until late. Taddeo (Tonio) appears and declares his love for her. Harlequin arrives, throws Taddeo out and the lovers sit down to eat. Taddeo returns to warn them that Pagliaccio is coming. Pagliaccio (Canio) comes in right on time to hear Colombina say to Harlequin the same words he heard Nedda tell her lover earlier that afternoon. Canio is unable to remain in character, and insists of finding out the name of Nedda’s lover. She improvises, trying to keep the play going, but Canio cries out he is not Pagliaccio any more. When she refuses once again to reveal her lover’s name, the jealously–mad Canio stabs her. As Silvio rushes from the audience, Canio stabs him as well. La commedia e finita.