Scene 1: Iago enters in mysterious dialogue with Roderigo. They noisily wake Brabantio (Desdemona's father), Iago making Roderigo tell of Desdemona's elopement. Brabantio expresses grief/anger.
Scene 2: Othello learns from Cassio of a problem in Cyprus, while Brabantio wants to attack Othello, or arrest him. The Duke is in Council, they all go there.
Scene 3: The Council hear that the Turks seem to be attacking Cyprus, decide to give the command to Othello, who enters with Brabantio who complains his daughter has been bewitched. Othello's defence. The story of their meeting. Desdemona comes, explains her position between father and husband. Duke tries to make peace. Desdemona demands to go to Cyprus with her husband. Final dialogue between Iago and Roderigo, followed by Iago's soliloquy: "I hate the Moor."
Scene 1: The boats arrive in Cyprus, after a great storm, one by one, Othello last, after conversations between Desdemona and Iago etc.. Iago and Roderigo talk, Iago persuades Roderigo that Cassio should be removed. Soliloquy of Iago tells his plan to make Othello jealous of Cassio.
Scene 2: A proclamation of celebrations.
Scene 3: During the celebrations, Iago makes Cassio drink (he cannot take wine), Roderigo provokes a quarrel, Cassio wounds Montano who tries to restrain him. Othello restores order, asks Iago who started it, Othello takes Cassio's rank from him. Iago comforts Cassio, encourages him to ask Desdemona to intercede for him. Iago's "Divinities of Hell" soliloquy.
Scene 1: Interlude with musicians. Iago and Cassio talk, Emilia helps Cassio.
Scene 2: Othello, in charge of the city, goes walking.
Scene 3: Desdemona tells Cassio she will help him; Othello and Iago see Cassio leave her, Iago says, "I like not that." Desdemona asks Othello to take Cassio back, insists. Iago and Othello talk, bringing the destruction of Othello's trust (line 246 "Why did I marry?"). Desdemona comes to fetch Othello...