Having told Othello that he knows for a fact that Cassio is in possession of Desdemona’s handkerchief, Iago makes light of the situation, arguing that once ownership of the handkerchief changes hands from Othello to Desdemona that Othello should be content to let the fate of the handkerchief lie entirely to Desdemona’s discretion. Unconsoled, Othello struggles to keep himself from losing consciousness (so worked up is he) only to lose consciousness when Iago relates a made-up chat that he had had with Cassio during which Cassio boasts of his mastery of Desdemona’s affections. At this point, Cassio joins Iago and offers to lend assistance in reviving the General only to be dissuaded by Iago who argues that a coma is better left to run its course, and, seeing the General coming to, he persuades Cassio to absent himself from the General for now, but to stay nearby as Iago would like a word with him. When Othello awakes, Iago urges him to conceal himself from view and to watch as Cassio relates his goings-on with Desdemona unto Iago. By and by, Othello conceals himself and observes Cassio boasting and laughing, unaware that the doting foolish woman of whom Cassio speaks is Bianca. Suddenly Bianca herself appears on the scene. Returning the handkerchief that Cassio had asked her to make a copy of, she leaves but not before accusing Cassio of having acquired it from his whore. At Iago’s behest, Cassio chases after Bianca to appease her.
At Iago’s suggestion, Othello decides to suffocate his wife in bed. Iago volunteers to dispatch of Cassio’s life. They are thus resolved when they are met by Lodovico, who is accompanied by Desdemona. He presents Othello with a letter from Venice. As Othello reads, Lodovico supposes, for Desdemona's benefit, that the letter is a summons for Othello to return to Venice which would, in the process, deputize the command of the Venetian forces in Cyprus to Lieutenant Cassio. The supposition pleases Desdemona which in turn angers Othello. Confused, Desdemona makes a gesture of reconciliation only to be struck across her face. Shocked, Lodovico pleads Othello to make amends, but Othello is unrepentant.
Othello is so sure of himself that he dismisses Emilia’s contention, as a likely cover story, that Desdemona is as innocent of committing lechery as a new-born babe is innocent of harboring an inveterate malice. Indeed, Othello is so sure of himself that he has Desdemona brought before him for the purpose of offering her salvation. That Desdemona refuses the offer, having no reason to seek it, dismays Othello who starts to weep. Othello offers it once more, in vain, before leaving in a state of despairing rage. Bewildered, Desdemona weepingly confides in Iago who chastises Emilia when Emilia suggests that a scurvy, rascally villain has abused Othello. Assuring Desdemona that a knotty problem concerning state affairs must be the cause of Othello’s distemper, Iago parts from Desdemona's company when he is accosted by Roderigo who says that he has had enough dealing with Iago, that he--Roderigo--is going to redeem his jewelry directly from Desdemona, the jewelry he had entrusted Iago to give Desdemona, and failing that that he would seek satisfaction from Iago himself who has failed to meet his obligations to Roderigo. Feigning admiration, Iago commends Roderigo’s passion and dares him to use it, assuring Roderigo that by being bold he will brighten his prospects of acquiring Desdemona which at the moment is dim what with her imminent departure from Cyprus in Othello's company. Ever the fool, Roderigo is once again persuaded to go along with Iago.
Having had supper with both Othello and Lodovico, Desdemona returns to her room as per Othello's instructions . As she prepares for bed, she has a strange foreboding of her imminent death. Undaunted, Desdemona asks Emilia if there are women in the world who would actually cheat on their husbands and if Emilia herself would cheat if the reward for cheating was the world. Emilia answers yes on both counts, saying that if wives are wicked then their husbands are to blame for wives invariably take after their husbands‘ examples. Desdemona gently begs to differ.