Through the Leaves, Southwark Playhouse, London

Ann Mitchell is pretty much perfection in this deeply eloquent revival by Daniel Kramer of Through the Leaves, a 1976 play by the German dramatist Franz Xaver Kroetz. She plays – and brings out all the inner beauty of – Martha, a plain, self-employed tripe butcher (and there aren't many of those roles in the female repertoire) who, in her lonely fifties, starts an affair with Otto, a boorish, chauvinist, and slightly young-er factory worker, ripely embodied by Simon Callow.

Punctuated and propelled forward by Martha's diary entries, the piece creates a strange mood – its poignancy strengthened, rather than compromised, by its unflinching eye for the grotesque comedy of the situation. A man is scarcely an ideal catch who tells his new lover that there's nothing remotely womanly about her and that she reminds him of all those Russian blokes who pretend to be female in order to win medals.

Callow's gruff, jaw-jutting presentation of this figure verges, at moments, on parody. More often, though, the slightly orotund tough-act feels just right – suggesting a weak, needy man who would like to come across as Bill Sykes. There are terrible imbalances of power in the relationship. She has financial independence and work she loves ("That's unnatural" chips in Otto, who wields the word like a cosh), but she's been so busy that she's let the emotional side of her life run on empty. Indeed, solitude seems to surround Ms Mitchell like a private atmosphere. His alleged advantages would seem to boil down to the fact that he's male and can come and go as he chooses for what he calls "away matches". But the actors in this excellent two-hander also communicate the chemistry between the characters – the mutual need, the ability to share a laugh can rip through the miserable intensity. What's moving about Martha is her combination of honesty and romantic hope. She doesn't want roses, but she wants Otto to be a bit better than merely better than nothing. He, though, has his precious freedom to worry about.

The piercing irony is that the moment she breaks through this boozy, cocksure wastrel's defences, she's finished. That fact emerges in a beautiful sequence where, in an effort to make herself more attractive, she bathes under a sun lamp. He criticises her for not wearing the prescribed glasses and she replies that it's because she doesn't want to have white bits round her eyes and spoil the effect for him. He insists that she put them on and rehearses his belief that women should stick by the rules. But you can tell that it's also because he is beginning to feel concern for her. His sense of himself would, however, never survive the indignity of caring for another, and so he vanishes. If Martha breaks your heart, he pains you, too, as the more trapped and pathetic individual.

Anthony Vivis's sharp translation has some nice comic turns. I also liked the blithe cultural obliviousness that makes Martha ascribe bath-house geishas to China. It reminded me of the bit in an Alan Bennett TV play where Thora Hird accepts a chocolate from a non-English-speaking Chinese. Popping it in her mouth, she turns to another woman and says, "Mmm. It'll take more than a box of Dairy Milk to erase the memory of Pearl Harbor."

To 8 Feb (020-7620 3494)