Feste and Sir Andrew both mistake Sebastian for Caesario - so does Olivia, and Sebastian thinks Olivia is rather lovely. Maria and Feste continue their attempts to make Malvolio think he's mad, meanwhile Sebastian starts to think he might be mad himself as everyone is treating him very strangely (because they all think he is Caesario.) Olivia asks Sebastian to marry her, and even though he doesn't know her very well, and she thinks he is Caesario, he agrees!