Duke Orsino is hopelessly in love with Olivia, a beautiful noble lady who is in grief for her brother's recent death. Orsino sent his servant, Valentine, to give his affections to Olivia, but Valentine returned saying that Olivia will continue to mourn for his brother for the next seven years. Olivia refuses Orsino to see her which makes Orsino heartbroken.
She doesn't understand how deeply I love her. My heart feels broken!
But from her handmaid do return this answer. (1.1.27)
After her brother died, Olivia cries every day in deep agony and rejects all messengers and people who wanted to see her.
Close the door and leave me alone!
Madam, food is ready for you. Please eat some..
Meanwhile. After a terrible shipwreck, Viola got separated from her brother and was saved by the Captain. They landed in Illyria, and Viola believes her brother is still alive. The Captain told Viola about Duke Orsino, and Olivia's similar situation with her. Viola decides to serve Orsino as a man and conceal her true identity.
Conceal me what I am, and be my aid. For such disguise as haply shall become. The form of my intent. I’ll serve this duke. (1.2.56-58)
Be you his eunuch, and your mute I’ll be. When my tongue blabs, then let mine eyes not see. (1.2.65-66)