The play is set in motion when Othello, a heroic black general in the service of Venice, appoints Cassio and not Iago as his chief lieutenant. Jealous of Othello's success and envious of Cassio, Iago plots Othello's downfall by falsely implicating Othello's wife, Desdemona, and Cassio in a love affair. With the unwitting aid of Emilia, his wife, and the willing help of Roderigo, a fellow malcontent, Iago carries out his plan. Making use of a handkerchief belonging to Desdemona and found by Emilia when Othello has unwittingly dropped it, Iago persuades Othello that Desdemona has given the handkerchief to Cassio as a love token. Iago also induces Othello to eavesdrop on a conversation between himself and Cassio that is in fact about Cassio's mistress, Bianca, but which Othello is led to believe concerns Cassio's infatuation with Desdemona. These slender “proofs” confirm what Othello has been all too inclined to believe—that, as an older black man, he is no longer attractive to his young white Venetian wife. Overcome with jealousy, Othello kills Desdemona. When he learns from Emilia, too late, that his wife is blameless, he asks to be remembered as one who “loved not wisely but too well” and kills himself.

For a discussion of this play within the context of Shakespeare's entire corpus, see William Shakespeare: Shakespeare's plays and poems (Shakespeare, William).