The scene opens with Iago complaining to Roderigo about his commander, Othello passing him over to promote Cassio, a young, handsome man to become his lieutenant. Iago then vows to exact his revenge. First, Iago has Roderigo tell Brabantio, Desdemona’s father that his daughter left to be married to Othello. Brabantio is opposed to this since Othello is Moor. He confronts Othello, and they forward their dispute to their Duke who had summoned Othello to send him to Cyprus to stop an invasion. The Duke permits Desdemona to sail with Othello after being convinced of their love. By the time the lovers get there the threat is already gone.
Iago makes Cassio drunk and has Roderigo engage him in a street brawl. Cassio’s rank is stripped for misbehavior, and therefore Iago gets his vengeance on him. Iago goes on to try and convince Othello of his wife’s unfaithfulness. He convinces Cassio to have Desdemona convince Othello to have him reinstated. Next, Iago makes a suggestion to Othello about Cassio and his Desdemona being lovers. Othello’s jealousy makes him angry. He has Iago promoted and asks for his help in killing Desdemona and Cassio.
Iago goes ahead to Cassio’s room and plants Othello’s wife’s handkerchief. Cassio unknowingly gifts it to Bianca, his mistress. Seeing Bianca with Desdemona’s ascertains Othello’s suspicions of the affair, and he abuses Desdemona verbally in the presence of others.
Iago orchestrates Cassio’s death by the hands of Roderigo but this backfires, and Roderigo is wounded by Cassio. Cassio is stabbed in the leg by Iago. Othello hears Cassio’s cries and assumes Iago has killed him, so he goes home to kill his wife. Iago accuses his wife Bianca of injuring Cassio. He then kills Roderigo and goes on to send his wife Emilia to Desdemona to deliver the news of what happened.
Othello finds Desdemona sleeping, wakes her up and accuses her despite her protests. Emilia arrives, and Desdemona briefly revives and declares herself innocent and also declares Othello innocence in her demise. Iago arrives with the others, and Emilia backs Desdemona’s guiltlessness and recognizes that Iago had been behind all of it. Othello finds out the truth and swears to kill him. However, then Iago takes Emilia’s life and flees. Othello commits suicide out of guilt, and Iago gets seized.