In Cyprus, Iago plots against Othello, planting the seed of doubt about Desdemona's fidelity and implicating Cassio as her lover. Using Roderigo, Iago arranges a fight that ultimately results in Cassio's demotion. Believing that his chances of reinstatement are better if he has Desdemona plead his case to her husband, Cassio, with Iago's help, arranges for a private meeting with Desdemona, who promises to speak on his behalf to Othello until his reconciliation with Othello is achieved.
As Cassio leaves, Iago and Othello appear. Othello notices Cassio's speedy departure, and Iago quickly seizes the opportunity to point out that Cassio seems to be trying to avoid the Moor. Desdemona immediately and enthusiastically begins to beg Othello to pardon Cassio, as she promised, and will not stop her pleading until Othello, preoccupied with other thoughts, agrees. The moment Desdemona and Emilia leave, however, Iago begins to plant seeds of doubt and suspicion in Othello's mind.
Othello, beset by uncertainty and anxiety, later demands of Iago some proof that Desdemona is unfaithful. Using a handkerchief that Desdemona later innocently drops, Iago convinces Othello that she has been unfaithful, and he stages a conversation with the innocent Cassio that further hardens the Moor's heart against his wife and her supposed lover. Convinced of his wife's betrayal and enraged and grieving, Othello rushes into action, making an agreement with Iago that he, Othello, will kill Desdemona, and Iago will dispose of Cassio.
Desdemona, true to her word to Cassio, continues to plead on his behalf, unknowingly confirming to Othello her unfaithfulness. He accuses her of falseness, and Desdemona, not knowing what she has done to offend, can only assure him that she loves him.
