Iago and Roderigo prepare to ambush Cassio. Iago hides, reassuring Roderigo that he will help out if Roderigo can't finish the job. In an aside, Iago tells the audience that no matter what, he hopes to benefit from this messy situation. Whether Roderigo kills Cassio or vice versa (or, even better, if they kill one another), Iago will be happy.
Cassio enters; Roderigo tries to stab him, but misses. Cassio then draws on Roderigo and wounds him. Iago wounds Cassio in turn, and then disappears. Othello arrives on the scene, sees that Iago has done as he promised, and thinks Cassio is dead. This bolsters his resolve to see to Desdemona, and he exits.
Lodovico and Gratiano enter, hearing the cries of both wounded men, but they aren't sure what to do. They.....
