Act I. "The Lion's Mouth." Grand courtyard of the Ducal palace,
decorated for festivities. At back, the Giant's Stairway, and the Portico della Carta, with doorway leading to the interior of the Church of St. Mark. On the left, the writing-table of a public letter-writer. On one side of the courtyard one of the historic Lion's Mouths, with the following inscription cut in black letters into the wall:
FOR SECRET DENUNCIATIONS TO THE INQUISITION AGAINST ANY PERSON, WITH IMPUNITY, SECRECY, AND BENEFIT TO THE STATE.
It is a splendid afternoon in spring. The stage is filled with holiday-makers, monks, sailors, shipwrights, masquers, etc., and amidst the busy crowd are seen some Dalmatians and Moors.
_Barnaba_, leaning his back against a column, is watching the people. He has a small guitar, slung around his neck.
The populace gaily sings, "Feste e pane" (Sports and feasting). They dash away to watch the regatta, when _Barnaba_, coming forward, announces that it is about to begin. He watches them disdainfully. "Above their graves they are dancing!" he exclaims. _Gioconda_ leads in _La Cieca_, her blind mother. There is a duet of much tenderness between them: "Figlia, che reggi il tremulo" (Daughter in thee my faltering steps).
_Barnaba_ is in love with the ballad singer, who has several times repulsed him. For she is in love with _Enzo_, a nobleman, who has been proscribed by the Venetian authorities, but is in the city in the disguise of a sea captain. His ship lies in the Fusina Lagoon.
_Barnaba_ again presses his love upon the girl. She escapes from his grasp and runs away, leaving her mother seated by the church door. _Barnaba_ is eager to get _La Cieca_ into his power in order to compel _Gioconda_ to yield to his sinister desires. Opportunity soon offers. For, now the regatta is over, the crowd returns bearing in triumph the victor in the contest. With them enter _Zuàne_, the defeated contestant, _Gioconda_, and _Enzo_. _Barnaba_ subtly insinuates to _Zuàne_ that _La Cieca_ is a witch, who has caused his defeat by sorcery. The report quickly spreads among the defeated boatman's friends. The populace becomes excited. _La Cieca_ is seized and dragged from the church steps. _Enzo_ calls upon his sailors, who are in the crowd, to aid him in saving her.
At the moment of greatest commotion the palace doors swing open. From the head of the stairway where stand _Alvise_ and his wife, _Laura_, who is masked, _Alvise_ sternly commands an end to the rioting, then descends with _Laura_.
_Barnaba_, with the keenness that is his as chief spy of the Inquisition, is quick to observe that, through her mask, _Laura_ is gazing intently at _Enzo_, and that _Enzo_, in spite of _Laura's_ mask, appears to have recognized her and to be deeply affected by her presence. _Gioconda_ kneels before _Alvise_ and prays for mercy for her mother. When _Laura_ also intercedes for _La Cieca_, _Alvise_ immediately orders her freed. In one of the most expressive airs of the opera, "Voce di donna, o d'angelo" (Voice thine of woman, or angel fair), _La Cieca_ thanks _Laura_ and gives to her a rosary, at the same time extending her hands over her in blessing.
She also asks her name. _Alvise's_ wife, still masked, and looking significantly in the direction of _Enzo_, answers, "Laura!"
"'Tis she!" exclaims _Enzo_.
The episode has been observed by _Barnaba_, who, when all the others save _Enzo_ have entered the church, goes up to him and, despite his disguise as a sea captain, addresses him by his name and title, "Enzo Grimaldo, Prince of Santa Fior."
The spy knows the whole story. _Enzo_ and _Laura_ were betrothed. Although they were separated and she obliged to wed _Alvise_, and neither had seen the other since then, until the meeting a few moments before, their passion still is as strong as ever. _Barnaba_, cynically explaining that, in order to obtain _Gioconda_ for himself, he wishes to show her how false _Enzo_ is, promises him that he will arrange for _Laura_, on that night, to be aboard _Enzo's_ vessel, ready to escape with him to sea.
_Enzo_ departs. _Barnaba_ summons one of his tools, _Isèpo_, the public letter-writer, whose stand is near the Lion's Mouth. At that moment _Gioconda_ and _La Cieca_ emerge from the church, and _Gioconda_, seeing _Barnaba_, swiftly draws her mother behind a column, where they are hidden from view. The girl hears the spy dictate to _Isèpo_ a letter, for whom intended she does not know, informing someone that his wife plans to elope that evening with _Enzo_. Having thus learned that _Enzo_ no longer loves her, she vanishes with her mother into the church. _Barnaba_ drops the letter into the Lion's Mouth. _Isèpo_ goes. The spy, as keen in intellect as he is cruel and unrelenting in action, addresses in soliloquy the Doge's palace. "O monumento! Regia e bolgia dogale!" (O mighty monument, palace and den of the Doges).
The masquers and populace return. They are singing. They dance "La Furlana." In the church a monk and then the chorus chant. _Gioconda_ and her mother come out. _Gioconda_ laments that _Enzo_ should have forsaken her. _La Cieca_ seeks to comfort her. In the church the chanting continues.