Othello Act 2, Scene 3: "The citadel."
Othello and Desdemona celebrate their love, while Iago offers Cassio some wine. He turns it down, stating that he does not drink, and then summons the married couple. Iago states, in soliloquy, his intentions to frame Cassio for making passes at Desdemona, and complains of watching the lovesick Roderigo sad with loneliness. Iago manages to get Cassio drunk and the gentlemen all sing songs of valor and joy to one another and in praise of Othello. Cassio mumbles that he, the Lieutenant, must be saved before the Ensign. Iago, the Ensign, is silently angered by this. Cassio leaves the festivities proclaiming his soberness in an overtly drunken fashion, allowing Iago to tell Montano of his worries about Cassio's ability to govern. Iago tells Roderigo to follow the drunken Cassio.
As Montano and Iago discuss their concern about Othello's rule during the drunken festivities, Cassio and Roderigo enter enraged. In a futile attempt to keep order, a drunken Cassio strikes Montano, injuring him to the death, and causing a grand scene for all of Cyprus to see. Iago tells him slyly that "You [Cassio] will be shamed forever!" Act 2, Scene 3. Othello enters and witnesses the raucous brawl, asking "Honest Iago" what occurred. Iago plays along amiably with the conversation, allowing Cassio to admit his guilt and Montano to die gracefully and with honor. Othello painfully dismisses his beloved lieutenant from office and requests his exit.
Cassio complains that he is mortally injured because he has lost his reputation, to which Iago replies, "Reputation is an idle and most false imposition; often got without merit and lost without deserving. You have lost no reputation at all, unless you repute yourself such a loser. What, man! There are ways to recover the General again" Act 2, Scene 3. Iago tells him that, instead of begging Othello to return him to his post, that he must befriend Othello's beloved wife, Desdemona. In harboring a close relationship with her, he will be reunited with the General Othello and reclaim his station.
Iago proclaims that he will set a trap for Cassio, Othello, and Desdemona, in which he plans to make Othello jealous of Cassio and Desdemona, for she is a weak female body and thus easily manipulated. Roderigo tells Iago that he will return to Venice, and Iago plans to bring his wife to Cyprus to unknowingly aid in his scheme.