1.1 Iago tells Roderigo about Othello's marriage. Together they rat out Othello and Desdemona to Desdemona's father.
1.2 Iago warns Othello that Desdemona's father is coming.
1.3 After the Duke approves the marriage, Roderigo wants to give up and drown himself. Iago convinces him that he can still get Desdemona in the end. Iago decides to convince Othello that Desdemona's cheating on him.
2.1 Iago arrives at Cyprus with Desdemona and his own wife, Emilia. To amuse Desdemona, Iago says lots of nasty, clever things about women. Later, Iago convinces Roderigo that Cassio and Desdemona are getting it on, and decides that he will use Cassio to make Othello jealous. He convinces Roderigo to fight with Cassio in order to get Cassio in trouble.
2.3 Iago gets Cassio drunk, watches him get into a brawl, and then tells Othello all about it. After Cassio is fired, Iago suggests to him that he ask Desdemona to intervene with Othello in his favor. Cassio thinks this is a great idea. Iago gloats about how well his plan is working.
3.1 Iago makes sure his wife will bring Cassio in to talk with Desdemona.
3.2 Iago and Othello tour the city.
3.3 Iago begins with small comments and gradually reels Othello in until he tells him point blank that Desdemona is cheating on him. Othello demands proof and Iago promises to give him some. Then Iago swears that he will help Othello revenge himself on Desdemona.
3.4 Iago comes in with Cassio and finds Desdemona upset at Othello's weird behavior. He promises her he will find out what's wrong.
4.1 Iago stages a conversation with Cassio such that Othello, overhearing, thinks they're talking about Desdemona. In fact, they're talking about a prostitute (Bianca) who is in love with Cassio.
4.2 Iago convinces Roderigo that he should kill Cassio.
5.1 Iago watches Roderigo try to kill Cassio. Then Iago stabs Cassio from behind. When more of Othello's soldiers appear, Iago stabs Roderigo too, as if trying to help Cassio. Then Iago tries to pin all the blame on Bianca, Cassio's prostitute lover.
5.2 After Othello strangles Desdemona, Emilia starts to realize what Iago has done. He tells her to shut up, but she tells Othello and everyone present that Iago is to blame for the whole situation. Othello tries to stab him, but instead Iago stabs Emilia and runs out. He's captured and brought back in, but he refuses to explain why he did all these terrible things. He swears he will never speak again.