Viola, shipwrecked and separated from her (of course) twin brother, seeks to make a life for herself in Illyria at the court of Duke Orsino, disguised, (well, obviously) as a young man. There she finds a highly unlikely bunch of characters including Sir Toby Belch and Sir Andrew Aguecheek, a couple of drunken members of the household of the lady Olivia, who (you've guessed it) immediately falls in love with her. One of the greatest subplots ever written centres on Olivia's arrogant steward, Malvolio, who is led to believe that she, Olivia, (keeping up?) loves him, with, as they say, hilarious consequences.