Twelfth Night.

Viola and Sebastian are lookalike twins, separated by a shipwreck. Viola lands in Illyria, where she disguises herself like her brother and goes into the service of the Duke Orsino. Orsino sends her to help him woo the Lady Olivia, who doesn't want the Duke, but finds that she likes the new messenger the Duke's sending. Then, of course, Viola's brother shows up, and merry hell breaks loose. Meanwhile, Olivia's uncle and his cohorts are trying to find some way to get back at Olivia's officious majordomo, Malvolio.