Lightning, thunder, gale force wind.
On a stormy evening, the people of Cyprus anxiously await the arrival of the new governor, Otello, from a naval battle with the Turks. For a moment it seems as if Otello's ship will founder, but Otello arrives safely and announces that the Turkish fleet has been destroyed, and the Cypriots greet him.
Iago, Otello's treacherous ensign, offers to help the young Venetian gentleman Roderigo in his seduction of Otello's wife, Desdemona – Iago envies Otello’s success and longs to destroy the Moor. Among his grievances, Iago is outraged that Otello has appointed Cassio to be the captain of the navy, a position that Iago hoped to have. The people of Cyprus celebrate the safe return of Otello and his men by lighting a bonfire.
Iago pressures Cassio to drink a toast to Otello and Desdemona. Cassio gives in. Cassio is drunk and barely able to stand upright. Iago lies to Montano, telling him that this is how Cassio spends every evening. Roderigo laughs at Cassio's drunkenness and Cassio attacks him. He draws his sword, Montano interferes, Cassio and Montano begin to duel. Iago sends Roderigo to call the alarm. Montano is wounded and the fight is stopped only by the appearance of Otello.
Otello orders Montano and Cassio to lower their swords. When Otello discovers that Montano is wounded, he becomes enraged. Desdemona enters, and, upon seeing that his bride's rest has been disturbed, Otello declares that Cassio is no longer Captain. The Cypriots leave Otello alone with Desdemona.
Together Otello and Desdemona recall why they fell in love. Desdemona prays that their love will remain unchanged. They kiss, overcome with love for each other.
The hall in the castle. Iago suggests to Cassio that he should ask Desdemona to talk to Otello about his demotion; Desdemona can influence her husband to reinstate him.
Desdemona and Emilia can be seen walking in the garden. Cassio approaches Desdemona. Watching from the room, Iago voices his nihilistic beliefs and hatred of humankind.
Otello enters the room; Iago, pretending not to notice him, says that he is deeply troubled. Cassio sees Otello from afar and goes discreetly away. Otello asks what's wrong, but Iago gives only vague answers. Finally, he hints that Cassio and Desdemona are having an affair. Otello begins to get suspicious. Iago warns Otello against jealousy, but also advises him to be vigilant.
A crowd of children, sailors, and Cypriots sing to Desdemona, praising her beauty and purity. They present her with gifts and wish her happiness before leaving.
Desdemona carries Cassio's request for reinstatement to Otello. Otello sourly tells her to ask him another time; as she persists, he grows impatient and says he has a headache. Desdemona offers to wrap his head in a handkerchief, Otello once gave her. Otello throws it to the ground and says he doesn't need it. Emilia picks up the handkerchief. Desdemona asks for Otello's forgiveness. Aside, Iago demands that Emilia give him the handkerchief. When she refuses, Iago forcibly takes it from her.
Otello dismisses the others, and declares that he now believes that Desdemona may be deceiving him. Iago returns, and the jealous Otello demands proof of Desdemona's infidelity. Iago says that once, when he and Cassio were sleeping in the same room, he heard Cassio talking to Desdemona in a dream. In the dream, says Iago, Cassio told Desdemona that they must be careful to conceal their love. Iago says that dreams don't prove anything, but remarks that he saw Cassio carrying Desdemona's strawberry-embroidered handkerchief just the day before. Otello swears vengeance on Desdemona and Cassio, and Iago joins him in his vow.
The great hall of the castle. Othello and Iago are talking in the hall as a herald enters.
A herald brings news of the approach of ambassadors from Venice. Iago explains to Otello that he will lure Cassio here and talk with him while Otello watches, hidden. He leaves to go get Cassio.
Desdemona enters and reminds Otello of Cassio's request. Otello says that his headache has returned, and asks Desdemona to wrap her handkerchief around his head. When Desdemona produces a different handkerchief, Otello demands the one with strawberries. When she says she does not have it, Otello says that it was a talisman. Desdemona says that he is trying to ignore Cassio's plea, and as she asks him about Cassio, he demands the handkerchief ever more insistently. Desdemona protests that she is faithful.
Otello laments his fate. When Iago calls out "Cassio is here!" Otello hides as Iago and Cassio enter. Cassio says he had hoped to see Desdemona here, for he wanted to know whether she had been successful with Otello. Iago asks him to tell of his adventures with that woman, Bianca. As Cassio laughs about his romantic adventures with Bianca, Otello assumes he is speaking of Desdemona. In a conversation only partially heard, Cassio seems to be telling Iago that another woman, a secret admirer, left him a handkerchief as a token. At Iago's urging, Cassio produces it, whereupon Iago seizes it—for it is Desdemona's—and holds it out where he knows Otello can see it. He then returns it to Cassio and teases him, while in his hiding place Otello fumes. Bugles sound, announcing the arrival of the Venetian ambassador, Lodovico. Iago warns Cassio that he should leave unless he wants to see Otello. Cassio exits, and Otello asks Iago how he should kill his wife. Iago advises Otello to kill Desdemona by suffocating her in her bed, while he will take care of Cassio. Otello promotes Iago to Captain.
Lodovico, Desdemona, Emilia, Roderigo, and other dignitaries enter. When Lodovico notes Cassio's absence, Iago tells him that Cassio is out of favor. Desdemona interrupts, telling Lodovico that she hopes he will soon be restored. Otello calls her a demon and almost strikes her violently but is held back by Lodovico. Otello then calls for Cassio. ("The Doge and the Senate greet the triumphant hero".) Cassio enters and Otello reads (mixing in insults to Desdemona) a letter from the Doge, announcing that he (Otello) has been called back to Venice and Cassio is to succeed him as governor of Cyprus. Enraged, Otello throws Desdemona to the ground.
The various characters express their feelings: Emilia and Lodovico express their sympathy for Desdemona, Cassio marvels at his sudden change of fortune, and Roderigo laments that Desdemona will soon depart. Iago is going to take care of Cassio. He advises Roderigo that the only way to prevent Desdemona from leaving is for Cassio, the new Duke, to die, and suggests that Roderigo will murder Cassio that night. In a fury, Otello orders everyone to leave. Desdemona goes to comfort him, but Lodovico pulls her away as Otello curses her. As the others leave, Otello collapses.Outside the crowd of Cypriots calls out victory and glory for Otello. ("Begone".) Iago presses Otello's forehead with his heel, then walks away.
Desdemona's bedchamber. Desdemona is preparing for bed with the assistance of Emilia. Desdemona wants to be buried in the bridal gown. Emilia tells her not to talk about such things. Desdemona recalls how her mother's servant Barbara was abandoned by her lover, and how she used to sing the Willow Song ("Singing, she wept on the lonely hearth"). After Emilia leaves, Desdemona prays (Ave Maria) and then falls asleep.
Silently, Otello enters, with a sword. He kisses his wife three times; she awakens. Otello asks her if she has prayed tonight; she must die, and he does not wish to condemn her soul. She asks God for mercy, both for her and for Otello. Otello accuses her of sin. Desdemona denies it and pleads for mercy, but Otello tells her it's too late and strangles her
Emilia knocks at the door, announcing that Cassio has killed Roderigo. Desdemona softly moans and dies. Emilia calls Otello a murderer and calls for help. Iago, Cassio, and Lodovico enter. Emilia, horrified, explains that Iago stole the handkerchief from her—Cassio confirms that the handkerchief appeared mysteriously in his lodgings. Montano enters and says that Roderigo, with his dying breath, has revealed Iago's plot. Iago, brandishing his sword, runs away.
After he realizes what has happened, Otello grieves over Desdemona's death. He then stealthily draws a dagger from his robe and stabs himself. Before he dies, he drags himself next to his wife and kisses her. He lies dead next to Desdemona.