When he has gone, Gioconda, who, anticipating the fate that might befall the woman who has saved her mother, has been in hiding in the palace, hastens to Laura, and hands her a flask containing a narcotic that will create the semblance of death. Laura drinks it, and disappears through the curtains into the funeral chamber. Gioconda pours the poison from the vial into her own flask, and leaves the empty vial on the table.
The serenade ceases. Alvise re-entering, sees the empty vial on the table. He enters the funeral apartment for a brief moment. Laura is lying as one dead upon the bier. He believes that he has been obeyed and that Laura has drained the vial of poison.
The scene changes to a great hall in Alvise's house, where he is receiving his guests. Here occurs the "Dance of the Hours," a ballet suite which, in costume changes, light effects and choreography represents the hours of dawn, day, evening, and night. It is also intended to symbolize, in its mimic action, the eternal struggle between the powers of darkness and light.
Barnaba enters, dragging in with him La Cieca, whom he has found concealed in the house. Enzo also has managed to gain admittance. La Cieca, questioned as to her purpose in the House of Gold, answers, "For her, just dead, I prayed." A hush falls upon the fête. The passing bell for the dead is heard slowly tolling. "For whom?" asks Enzo of Barnaba. "For Laura," is the reply. The guests shudder. "D'un vampiro fatal l'ala fredda passò" (As if over our brows a vampire's wing had passed), chants the chorus. "Già ti vedo immota e smorta" (I behold thee motionless and pallid), sings Enzo. Barnaba, Gioconda, La Cieca, and Alvise add their voices to an ensemble of great power. Alvise draws back the curtains of the funeral chamber, which also gives upon the festival hall. He points to Laura extended upon the bier. Enzo, brandishing a poniard, rushes upon Alvise, but is seized by guards.
Act IV. "The Orfano Canal." The vestibule of a ruined palace on the island of Giudecca. In the right-hand corner an opened screen, behind which is a bed. Large porch at back, through which are seen the lagoon, and, in the distance, the square of Saint Mark, brilliantly illuminated. A picture of the Virgin and a crucifix hang against the wall. Table and couch; on the table a lamp and a lighted lantern; the flask of poison and a dagger. On a couch are various articles of mock jewelry belonging to Gioconda.
On the right of the scene a long, dimly lighted street. From the end two men advance, carrying in their arms Laura, who is enveloped in a black cloak. The two cantori (street singers) knock at the door. It is opened by Gioconda, who motions them to place their burden upon the couch behind the screen. As they go, she pleads with them to search for her mother, whom she has not been able to find since the scene in the House of Gold.
She is alone. Her love for Enzo, greater than her jealousy of Laura, has prompted her to promise Barnaba that she will give herself to him, if he will aid Enzo to escape from prison and guide him to the Orfano Canal. Now, however, despair seizes her. In a dramatic soliloquy—a "terrible song," it has been called—she invokes suicide. "Suicidio! ... in questi fieri momenti tu sol mi resti" (Aye, suicide, the sole resource now left me). For a moment she even thinks of carrying out Alvise's vengeance by stabbing Laura and throwing her body into the water—"for deep is yon lagoon."
Through the night a gondolier's voice calls in the distance over the water: "Ho! gondolier! hast thou any fresh tidings?" Another voice, also distant: "In the Orfano Canal there are corpses."
In despair Gioconda throws herself down weeping near the table. Enzo enters. In a tense scene Gioconda excites his rage by telling him that she has had Laura's body removed from the burial vault and that he will not find it there. He seizes her. His poniard already is poised for the thrust. Hers—so she hopes—is to be the ecstacy of dying by his hand!