Twelfth night, Donmar Warehouse, London

Harrowing hilarity

He looks as though his copious blubber has been constrained from birth in a wing collar and buttoned-up pinstripe suit and that he must have emerged from the womb with that self-important beard and punctilious moustache. His gait is an effeminately officious cross between a march and a scamper; his tone is a prissily sibilant sneer; and he is forever consulting his watch with righteous impatience. At night, his locks are lovingly protected by a lady's hairnet.

And yet, Simon Russell Beale's magnificent Malvolio, the killjoy Puritan steward, is by no means a straightforward figure of fun in this deeply diverting Twelfth Night, directed by Sam Mendes in a spare, warmly candle-lit staging, with a cast in costumes that range from the Edwardian era to the Thirties. No one is better than Russell Beale at showing you the terrible, tragic intensity of people who haplessly fall short of tragedy, nor at suggesting a core of massively affronted dignity in the midst of preposterous mayhem.

This Twelfth Night now joins in rep, with the same crack ensemble, Mendes's acclaimed production of Uncle Vanya. Both are plays of bruised illusions, unrequited love and frustratingly misdirected sexual desire. They have comparably shifting, precarious moods, the comedy shot through with melancholy. Twelfth Night has been described as the most Chekhovian of Shakespeare's comedies. Thanks to Russell Beale, who performs both roles, and to Mendes's acute direction, Malvolio here accrues a depth of abused humanity that bears comparison with that of Vanya, the counterpart steward in the Chekhov.

It's a brilliant touch that, in this production of Twelfth Night, the scene where Malvolio is gulled with the forged letter takes place not in the garden but in his bedroom, with the tricksters behind a screen, watching him as he reclines lost in goggle-eyed, pitifully grandiose fantasies on his barren single bed. The effect of the letter is brilliantly funny, but the setting makes the episode feel like a nasty violation of privacy. And it's painful to watch the quiet, fixated sincerity with which this Malvolio slumps to his knees and addresses the apparition of Olivia (the amusingly sexy Helen McCrory) in the silver picture frame at the back. And though Russell Beale is riotous as a born-again roué in the yellow cross-gartered stocking scene, the sheer force of his need and the epic scale of his deluded confidence give a harrowing edge to the hilarity.

The empty picture frame acts as a threshold and a kind of symbolic space where characters appear who are in the thoughts of others. Emily Watson's attractively understated Viola enters through this border on her arrival in Illyria. And when Antonio's confusion gives her hope that her twin brother has survived, Sebastian suddenly materialises within it behind her. Watson's half-smile and gently closed eyes, as she muses on this miraculous possibility, are extremely touching. And during the romantic reunions at the end, the frame keeps pointedly within our view the figure of the straitjacketed and blindfolded Malvolio, a spectacle which adds a modifying note of rebuke to the oblivious celebrations.

The production perhaps feels a little land-locked for a play of romantic redemption where "Tempests are kind, and salt waves fresh in love!", but it is full of imaginative strokes and details that make you ponder the play anew. There's a lovely moment, for example, when Anthony O'Donnell's podgy, tatterdemalion little Feste sings the line "I am slain by a fair cruel maid" and shrewdly looks at Viola in a way that suggests he has seen through her male disguise. Like Uncle Vanya, this Twelfth Night is booked solid, apart from a few tickets that can be queued for each day. If that fails, it would be well worth trying to tunnel your way in.

To 30 November (020-7369 1732). A version of this review appeared in later editions of Wednesday's paper