Act 1: The Lion’s Mouth
Venice in the 17th century, the courtyard of the Doge’s Palace
Outside the Doge’s Palace, citizens are celebrating Carnival with its regatta and gondola races. Among them is Barnaba, a spy for the Inquisition. A street singer known as La Gioconda crosses the square with La Cieca, her blind mother. Barnaba attempts to force his attentions on her, but Gioconda rejects him. Leaving her mother, in the courtyard, she sets off to find her lover, a sea captain by the name of Enzo.
Determined to have his revenge, Barnaba denounces La Cieca as a witch, accusing her of using her powers to influence the outcome of the races. Hearing the commotion, Gioconda returns with Enzo who struggles to restrain the mob from attacking the old woman.
Alvise Badoero, a leading member of the Venetian Inquisition, now arrives on the scene with Laura, his wife. As her husband quells the riot, Laura places La Cieca under her personal protection. As a mark of gratitude, the old woman presents Laura with her cherished rosary (“Voce di donna o di angelo”). Meanwhile, Barnaba has observed Laura and Enzo engaged in a furtive conversation. Recalling how Laura was once engaged to a now-banished Genoese nobleman by the name of Enzo Grimaldo, he puts two and two together.
Barnaba confronts Enzo, who confesses that he intends to take Laura away so they can begin a new life. Barnaba, who sees a chance to drive a wedge between the sea captain and the besotted Gioconda, offers to row Laura out to Enzo’s ship that night.
Enzo leaves and Barnaba puts his plan into action. Finding a scribe, he dictates a letter for Alvise in which he reveals Enzo’s real identity and Laura’s infidelity (“O monumento”). Finally, he drops the letter into the Lion’s Mouth, the place people deposit secret information for the Inquisition. What Barnaba doesn’t know is that he has been overheard by Gioconda who is horrified to learn of Enzo’s duplicity.
Act 2: The Rosary
The deck of Enzo’s ship anchored in the lagoon
Barnaba has rowed out to Enzo’s ship disguised as a fisherman where he entertains the crew by singing a barcarolle (“Pescator, affonda l’esca”). After he has left, Enzo arrives. As he waits for Laura to join him, he gazes into the night and reflects on the beauty of sky and sea (“Cielo e mar”). Barnaba returns in his boat with Laura and the lovers are reunited. She is nervous, however, and suspicious of Barnaba. After reassuring her, Enzo goes below deck to prepare for the ship’s departure. Laura prays to the Virgin to protect them (“Stella del marinar”).
Gioconda has followed, hoping to take her revenge on Laura. Appearing on deck, she confronts her enemy (“L’amo come il fulgor”). Brandishing a dagger, Gioconda is just about to strike when she catches sight of her mother’s precious rosary hanging around her rival’s neck. Realising that it must have been Laura who saved La Cieca, Gioconda decides to rescue her instead. Warning her that Alvise and his men will arrive at any moment, she bundles Laura into a boat and helps make good her escape.
Enzo returns to find Laura gone. Gioconda explains that it must have been Barnaba who betrayed them to the authorities and urges him to come back with her to the city. Alvise’s men approach, firing canons. Rejecting Gioconda, Enzo reaffirms his love for Laura. Rather than let it fall into the hands of his enemy, he orders his men to set fire to their own vessel before diving headfirst into the lagoon.
Act 3: The Ca’ d’Oro
Apprised of Laura’s plan to elope with Enzo, Alvise decides that only his wife’s death can restore his family honour (“Sì, morir ella de’!”). Laura arrives and Alvise demands she drink a vial of poison. Not only will she die, but by committing suicide she will condemn her soul to everlasting damnation.
Alvise leaves and Gioconda enters, having managed to slip into the palace. Determined for the sake of her former lover to save her rival once again, she gives Laura a potion that will make her appear to be dead while only putting her to sleep.
Members of the Venetian nobility, including Barnaba and Enzo in disguise, arrive at the palace for a spectacular entertainment (The Dance of the Hours). As the ballet reaches its climax, a funeral bell is heard. Barnaba drags in La Cieca who has been found praying over Laura’s body. Hearing that his beloved is dead, Enzo throws off his disguise and is arrested on the spot.
A desperate Gioconda now offers herself to Barnaba if he will secure Enzo’s release. Barnaba agrees, but not before taking La Cieca away with him as security. In a final gesture, Alvise parades his wife’s body in front of his appalled guests.
Act 4: The Orfano Canal
A crumbling ruin on the island of Giudecca
Gioconda has had Laura’s sleeping body carried off to her tumbledown home on the Giudecca. With her emotions fluctuating wildly between rage and despair, she contemplates taking her own life (“Suicidio!”).
Enzo arrives, believing that Gioconda has snatched Laura’s dead body from its resting place. He is about to stab her in a blind fury when he hears Laura’s voice in the next room. Reunited, the lovers thank Gioconda for her sacrifice before making good their escape.
The distant sounds of gondoliers’ voices herald Barnaba who arrives to claim his reward. Gioconda plays for time, pretending to welcome him while putting on her finest jewellery. At the last moment, however, she seizes a dagger and stabs herself. Bitter and enraged, Barnarda delivers one final bombshell. “Yesterday your mother offended me,” he screams. “I drowned her!” But Gioconda can no longer hear him.