What Is the plan that is being prepared?

Iago enters, and Cassio tells him that he means to speak to Desdemona, so that she may clear things up with Othello. Emilia comes out, and bids Cassio to come in and speak with Desdemona about his tarnished reputation. Iago means for Othello to see and Cassio together and then plants the seeds of doubt in Othello's mind.