Act III, Scene 4

Summary
       Desdemona and Emilia ask a clown where the Cassio's home is, the clown says he does not know, but and he will ask other people to find out. Desdemona tells the clown that once he had found Cassio, please ask him to find her and tells him that she had spoken for him to the general so that he should be able to get a satisfactory result.
      After the clown left,   Othello came to ask Desdemona for the handkerchief when she recalled about where she missed it.Othello explains the handkerchief’s history for her that an Egyptian woman gave it to his mother and told her that it would make her desirable and keep Othello’s father loyal, but if she lost it or gave it away, Othello’s father would leave her. Othello’s mother gave him the magic handkerchief on her deathbed, instructing him to give it to the woman he desired to marry. Desdemona is unsettled by the story and says that she has the handkerchief, but not with her. As he accuses her, demanding “The handkerchief!” with increasing vehemence, she entreats for Cassio as a way of changing the subject.

Emilia laments man's jealousy is scary after Othello left.  Meanwhile, Cassio and Iago enter and Cassio immediately continues to ask Desdemona for help. Iago promises that he will go soothe his master. Emilia speculates that Othello is jealous, but Desdemona maintains her conviction that Othello is upset by the political problem
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While Cassio's waiting for Othello, Bianca enters. She blames Cassio for infrequently visit her and he apologizes for that and says that's because he was under stress. He asks her to copy the embroidery of a handkerchief which he recently found in his room. Then they decide to meet later that evening.