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 odor. Enough; no more.
'Tis not so sweet now as it was before.
Twelfth Night opens on a panorama of grief. The twins, Viola and Sebastian, grieve for each other, thinking their sibling drowned in the shipwreck that separates them. The Countess Olivia grieves for her dead brother, refusing the Duke Orsino's advances on the grounds of mourning. Orsino grieves over Olivia's refusal, though it's not difficult to conceive that his bitterness, which wells up after he notes the "dying fall" of his musicians, may originate elsewhere.
Perhaps the comedic elements of Twelfth Night, then--Viola's disguise as Cesario, Sir Toby's antic pranking, and the arbitrary-seeming shuffling of romantic partners--suggest a darker element toward which the play's topsy-turvydom provides, if not a corrective, a brief respite. For those unfamiliar: Viola, shipwrecked on the Illyrian coast, disguises (for some reason) herself as a boy and becomes a servant of the Duke Orsino, with whom she falls madly in love. But Orsino only has eyes for Olivia, and unwittingly tortures Viola by sending her to repeatedly declare his love, a scheme which has the complicated consequence of sending Olivia head over heels for the disguised Viola.
In the B-plot, the pranksters Maria and Sir Toby Belch, along with their idiot friend Sir Andrew Aguecheek, gull the cheerless Malvolio, Olivia's steward, into believing that Olivia is in love with him. Malvolio is the only character who refuses to partake in the celebratory atmosphere of the play, and disapproves of such salubrious activities as carousing and joking, saying of Olivia's fool:
MALVOLIO: I marvel your ladyship takes delight in such a barren rascal. I saw him put down the other day with an ordinary fool that has no more brain than a stone. Look you now, he's out of his guard already. Unless you laugh and minister occasion to him, he is gagged. I protest I take these wise men that crow so at these set kind of fools no better than the fools' zanies.
OLIVIA: Oh, you are sick of self-love, Malvolio, and taste with a distempered appetite.
Malvolio, having wandered in from some other world and declared himself an enemy of laughter, probably gets what's coming to him. He is essentially cast in the play's masque against his will, convinced by a faked love letter that wearing a ridiculous get-up (yellow stockings with cross garters) and smiling ceaselessly will prove his love for Olivia. In an essentially comic play, this play would be sustained until Malvolio's utter embarrassment and possibly reform, but in Twelfth Night the prank results in Malvolio being cast into a madman's dungeon.
We might still laugh at Malvolio in this state, but our laughter is increasingly discomfiting, and undermines the relief that Twelfth Night has promised us. This is nothing compared to the sudden possibility of violence that Orsino threatens upon Viola, whom he has discerned is the object of Olivia's affection:
ORSINO: Why should I not, had I the heart to do it,
Like to th' Egyptian thief at point of death
Kill what I love?--a savage jealousy
That sometimes savors nobly. But hear me this:
Since you to nonregardance cast my faith,
And that I partly know the instrument
That screws me from my true place in your favor,
Live you the marble-breasted tyrant still.
But this your minion, whom I know you love,
And whom, by heaven I swear, I tender dearly,
Him will I tear out of that cruel eye
Where he sits crowned in his master's spite. --
Come boy, with me. My thoughts are ripe in mischief.
VIOLA: And I, most jocund, apt, and willingly,
To do you rest, a thousand deaths would die.
Suddenly, without warning, we are transported to Othello. Orsino's bloodlust is not so shocking; his overtures to Olivia have always had the air of a madman and a solipsist, but Viola's glee at the prospects of her death is one of the most unnerving moments I can think of in Shakespeare. Where are we, and what has comedy wrought? Of course, Sebastian shows up at the last minute to fix everything (conveniently becoming the new, more appropriate object of Olivia's affections) and Orsino marries the servant he was about to murder, his bride still in Cesario's breeches. But one wonders what the play might have been like if Sebastian had been just moments too late. It's true what they say, I suppose--in comedy, timing is everything.