Act I
Otello's ship survives a crashing storm to reach safe harbor as he returns in triumph from battle. Among the overjoyed crowd, only two scorn their general's success: Roderigo, in love with Otello's wife Desdemona; and Iago, jealous that Otello has promoted Cassio-not him-to the rank of lieutenant. Iago plots with Roderigo to bring about Cassio's downfall. With a rowdy drinking song, Iago gets Cassio completely drunk. Roderigo taunts Cassio until he is angry enough to draw his sword against any perceived insults. In the ensuing fight, Montano is wounded. Otello arrives in a fury, and when Cassio is unable to explain his actions, Otello strips him of his rank. Once the crowd has dispersed, Otello and his bride serenely recall the happiness of their first meeting with tender kisses.

Act II
Iago now sets his malicious sights on Otello. The unwitting Cassio, believing Iago to be his friend, agrees to ask Desdemona to obtain Otello's pardon for him. Iago actually plans to convince Otello that Desdemona and Cassio are secret lovers. Otello arrives to find Iago shaking his head in feigned disapproval while looking at Cassio and Desdemona conversing in the distance. Iago's deliberately evasive responses plant the first seeds of suspicion in Otello's mind, and when Desdemona arrives to speak in Cassio's favor, Otello is convinced that Iago's accusations of her infidelity must be true. When he and Otello are left alone, Iago now claims to have overheard Cassio talking in his sleep of his love for Desdemona and also to have seen Desdemona's handkerchief in Cassio's possession. Enraged, Otello swears to prove Desdemona's guilt and Iago joins him in an oath of vengeance.

Act III
Desdemona, at an utter loss to explain her husband's behavior, approaches him once more to plead for Cassio's reinstatement. Otello demands her handkerchief, remembering Iago's suggestion that she has given it to Cassio as a love token. When she is unable to produce the handkerchief (which has been pocketed earlier by Iago), Otello accuses her of adultery. Desdemona, swearing that she is innocent, flees from her husband's wrath. Iago hurries in with the news that Cassio is approaching and urges Otello to hide nearby. Otello is led to believe that Cassio's gossip about his sweetheart refers to Desdemona. To Otello's horror, Cassio shows Iago a lady's handkerchief that he found in his bed-Desdemona's handkerchief, secretly planted there by Iago. Otello determines that Desdemona is to die that very night. Later, in front of the Venetian ambassador and assembled populace, he denounces his wife as a whore as Iago gloats in triumph.

Act IV
Attended by Emilia, Desdemona uneasily waits for Otello as she sings the Willow Song, a poignant ballad of love and death. Sending Emilia away with a tearful farewell, she sinks into sleep. Otello enters, tortured by his conflict between love and revenge. He bends down to kiss her, and when Desdemona awakes, he solemnly asks her if she has said her prayers, for he would not want her to die unrepentant. Although Desdemona denies any involvement with Cassio, Otello strangles her in a fury. Emilia returns and, finding her mistress murdered, cries for help. Piecing together the truth, Otello realizes Iago's treachery and stabs himself. Kissing Desdemona, he dies.