(from Wikipedia, possible spoilers follow)
Othello, a Moor who has just eloped with the fair Desdemona when the play opens, leaves Venice to command the Venetian armies against the Turks on the island of Cyprus, accompanied by his new wife and his lieutenant, Cassio. When they arrive, they find that the weather has destroyed the Turkish fleet. Iago, a standard bearer, repeatedly tries to undo Othello, finally succeeding when he plants Desdemona's handkerchief on Cassio, managing to convince Othello that his wife has been unfaithful with the lieutenant. Othello kills Desdemona out of jealousy, before Iago's wife, Emilia, eventually reveals that Desdemona's affair was but an invention of Iago's. Iago immediately kills his wife also, and Othello then commits suicide in grief. At the end, it can be assumed, Iago is taken off to be tortured and executed.