The play opens in Venice, Italy, at night. In the opening scene, Iago complains that Othello, his Commander, has passed him over to promote handsome Cassio to be his Lieutenant. He vows to get revenge. Iago first asks his friend Roderigo to tell Desdemona's father Brabantio that his daughter has left to marry Othello, a marriage Brabantio opposes because Othello is a Moor (an African). Brabantio confronts Othello, and they take their argument to the Duke, who has summoned Othello to ask him to sail to Cyprus to stop a Turkish invasion. Convinced by Othello and Desdemona that they love each other deeply despite their differences, the Duke gives Desdemona permissionto travel with Othello. By the time they reach Cyprus the foreign threat is gone.
Iago has Roderigo got Cassio drunk and draw him into a street fight. Iago has his revenge on Cassio when Othello strips Cassio of his rank for misbehavior. Then Iago decidesto make Othello believe his wife is unfaithful. He encourages Cassio to ask Desdemona to plead with Othello to be reinstated. Iago suggests to Othello that Desdemona is Cassio's lover. Trusting Iago and mad with jealousy, Othello promotes Iago and asks Iago to help him kill Cassio and Desdemona.