Malvolio, dressed ridiculously and smiling grotesquely, appears before an astonished Olivia. Thinking him insane, she puts him in the care of Sir Toby, who decides to treat him as a madman by having him bound and put in a dark room. Toby also decides to deliver Sir Andrew’s challenge to Cesario in person in order to force the two of them into a duel. Terrified, they prepare to fight. At that moment, Antonio enters, thinks that Cesario is Sebastian, and comes to his defense. Antonio is immediately arrested by Orsino’s officers. Since he is sure that Viola is Sebastian, Antonio is bitter about the apparent denial of their friendship. Viola is herself delighted by Antonio’s angry words because, since he called her Sebastian, there is hope that her brother may in fact be alive.