"If music be the food of love, play on;
Give me excess of it, that, surfeiting,
The appetite may sicken and so die.
That strain again! it had a dying fall:
O, it came o'er my ear like the sweet sound
That breathes upon a bank of violets,
Stealing and giving odour!"
Shipwrecked and alone in a foreign land, Viola makes the best of the situation the only way she can — by disguising herself as a man named Cesario and landing a job as a page for the local Duke. Duke Orsino warms to Viola quickly, and entrusts her with a job, to woo the Countess Olivia, whom he's been pining for. But Viola does too good of a job, and soon Olivia has fallen head-over-heels for "Cesario."
All of that is before the members of Olivia's house convince her snobby right-hand man Malvolio that she secretly in love with him, and before Viola's twin brother shows up, bearing a striking resemblance to his sister when she's in drag...