Scene i: At the front of his headquarters, Othello talks to Iago, and he claims that he overhead Cassio saying Desdemona's name when he was sleeping. Othello believes everything that Iago tells him. Cassio arrives, and Iago sets him up by saying he will talk to him later. His plan is for Cassio talk to him about Bianca while Othello listens and thinks Cassio is talking about Desdemona. This plan works, and Othello hears from Cassio about how "she" loves him.

When Bianca arrives, the conversation incriminates Cassio more because seems that he gave Othello's handkerchief to Bianca. They leave the stage and Othello vows to kill Desdemona and Iago says that he will kill Cassio. Desdemona enters with news from Venice: Othello has been called there and Cassio will replace him as governor of Cyprus. Desdemona is happy, but Othello is mad and hits her. Iago tells the Venetian official Ludovico Othello hit his wife because he is troubled and they have a bad marriage Scene ii: At his citadel, Othello talks to Emilia, and she says that Desdemona never cheated on him. He tells Desdemona to come and calls her a whore; she doesn't understand this.

Othello leaves and Desdemona tells Emilia and her husband Iago that she is confused. When the two women leave, Roderigo comes. He complains that Iago took his money, and he is no closer to Desdemona's love than ever. Iago tells him that because Cassio is governor, Desdemona is going to be leaving for Venice.

To prevent this, Iago suggests that Roderigo kill Cassio, forcing Othello and Desdemona to remain on Cyprus. Scene iii: Othello orders Desdemona to go to bed and she does. Emilia talks shortly with Desdemona and she says she loves Othello, but now is afraid of him. Emilia says, that all husbands are impossible..