We're now at the pithy center of Twelfth Night, in particular Act II, scene 4, where Viola almost loses her decorum and her incognito--where, that is, she almost confesses her suppressed love for Orsino: "My father had a daughter loved sa man/As it might be perhaps,were I a woman,/ I should your lordship." This must be a hellaciously difficult scene to get right--so much going on that one (Viola) must conceal and the other (Orsino) seems barely to understand. This is perhaps the scene that makes the play so popular with some Shakespeare fans, despite its impossible plot and its unpleasant subplot. Orsino does not take the bait--or yet perhaps he does, without knowing it. For Viola becomes the one person (to our knowledge) who can actually command the attention of those most self-absorbed man. He seems to be taken by Viola better than he knows.
There follows the "boxwood" scene where Malvolio takes the bit of his own, finding the letter and determining to go before his lady cross-gartered and in yellow stalkings. Again, there are so many ways in which it could go wrong but here, perhaps the extraordinary artistry is in the writing, not the playing. Shakespeare does a remarkable job of keeping the practical joke all funny and engaging--the bad stuff comes later. I'm still struck by how similar and yet how different this "letter trap" is so similar and yet so different from what is, after, all, virtually the identical device just a few years before in Much Ado About Nothing.