Roderigo and Iago prepare with their swords to kill Cassio. Roderigo worries that he may fail and Iago states that he must not fail. At first he doesn't care whether the two kill one another; upon further thought, however, Iago realizes that Cassio must die in order to protect his own reputation. Cassio walks out into the street to Roderigo's challenge. Cassio wounds Roderigo, and then Iago wounds Cassio in the leg and escapes. Roderigo believes himself slain; Cassio believes himself maimed. Othello enters from above to witness the duel below. When he sees the injured Cassio, he believes that Iago has told him the truth, and soon exits.
Lodovico and Gratiano enter upon the confusion. Cassio screams 'murder,' as Roderigo believes that he will bleed to death unless someone summons a surgeon. Iago enters the street with a light to see what's going on. As Roderigo begs Iago for help, he stabs him in the dark so that nobody will see the murderer. Lodovico and Gratiano show the injured Cassio to Iago for aid, as Iago, the true perpetrator of this injury, attempts to bind his leg.
During the confusion, Bianca enters, wondering about the noise, and cries over her injured beloved, Cassio. Iago feigns innocence and questions both duelers about the events before they are brought offstage. Emilia enters, as well, to inquire about the commotion, and finds her husband with Bianca. Iago tells his wife that this chaos is the product of whoring, and the two insult Bianca before leaving to find Cassio. Iago states that "This is the night / That either makes me, or undoes me quite" Act 5, Scene 1.
