A shipwreck strands Viola on the coast of Illyria. She believes her twin brother Sebastian to have drowned. With no-one else to turn to she disguises herself as a man – taking the name ‘Cesario’ – and enters the household of Duke Orsino, whom she rapidly falls in love with. However, Orsino has fallen in love with the Countess Olivia, who is deep in mourning for her brother. Olivia refuses to be wooed by Orsino as she is in her mourning period. Orsino dispatches ‘Cesario’ in his place, to woo Olivia on his behalf. Olivia falls for ‘Cesario’ instead.

Meanwhile, Olivia’s steward Malvolio has made some enemies within her court due to his arrogance and sour self-importance. Sir Toby Belch (Olivia’s drunken uncle), Sir Andrew Aguecheek (Toby’s friend), and servant Maria, decide to trick Malvolio. They make him believe that Olivia secretly loves him. Not only that, but that she wants to see him smiling and wearing cross-gartered yellow stockings. Malvolio dutifully starts grinning and dresses accordingly – Olivia believes him to be mad as he looks so ridiculous. The conspirators lock him up, and enlist the fool – Feste – to mock Malvolio further.

Elsewhere in Illyria, Sebastian (Viola’s twin brother) is revealed to be alive and well. He has been rescued by a sea captain called Antonio, whose love for Sebastian leads him to accompany him to Illyria despite Orsino wanting to kill Antonio on account of past conflict between them.

Olivia bumps into Sebastian and mistakes him for ‘Cesario’. She asks him to marry her and Sebastian accepts. They are quickly married. This leads to immense confusion as ‘Cesario’ meets Olivia separately, and Sebastian runs into Orsino. Eventually, Viola reveals her identity and is reunited with Sebastian. Duke Orsino vows to marry Viola, Malvolio is released, and Sir Toby marries Maria.