Cassio is drunk due to Iago's insisting that he drink more. Roderigo insults Cassio and the two begin a chase. Montano tries to intervene. Cassio attacks Montano.
A brawl breaks out. Iago's plan is going according to his evil ideas. Iago pretends he is trying to intervene. After hearing an alarm going off, Othello comes into the area of the brawl. He demands that the brawlers stop.
Othello is highly upset with Cassio. He fires him on the spot. Desdemona is awakened. Othello is enraged that his love has come to stir about.
Iago pretends to be grieved about the whole brawl. Iago convinces Othello that he will be on guard and protect the peace.
Othello is forever grateful to Iago. Iago's plan is a success.
Next, Cassio is upset that his "reputation" is ruined. Iago plants the idea that Cassio can plead with Desdemona in order to be reinstated to his former position as lieutenant.