WC, Blue Elephant Theatre, London

There is something of the kitchen-sink drama - albeit transposed to a public urinal - about Antonio Ribeiro's imaginative but troubled morality play. The lavatory of the title is the private domain of two men locked in co-dependency - Ted, a wheelchair-bound toilet attendant, and Rob, a rough sleeper who uses the facilities. Rejected by their absent families, both fill this void in each other's lives - petty squabbles included.

Ted (a quietly tyrannical Cedric Duncan) is a pseudo-philosopher who makes the subterranean public convenience in which he works a kingdom for his own model of law and order. Morality, in this underworld, is held in a kind of limbo, somewhere between heaven and hell, tainted as it is by Ted's skewed sense of justice.

The inter-dependency and seemingly benign relationship between these social outcasts plays out well. Ribeiro effectively dupes his audience over Ted's motivation for helping the illiterate Rob to carry on a correspondence with his mother, and masks the latent violence of the slow-witted Rob (Phillip Goodchild). The question of just how much they are conspirators or self-seeking perpetually hangs in the balance until Ted and Rob's eventual clash. (The "Traitor" headline on the cover of one of Rob's Big Issue magazines, stashed on Ted's desk, almost lights up with irony as events turn darker.)

But the psychological verisimilitude of these two is lacking in the lesser characters - a clown and an evangelical preacher. Representatives of the secular and spiritual, they are essentially the blank canvas on whichTed tests out his bogus moral framework, and through whom Ribeiro explores man's craving for control.

Expecting nothing more than a quick slash from their visit to this WC, both are confronted by a new moral order, conceived by Ted and executed by his henchman, Rob. But the physicality of the ensuing fray (an unfortunate case of mistaken identity) lacks dexterity. The frenzied binding of the clown with industrial tape is not frenzied enough; the preacher's impotence as he witnesses events spiral out of control fails to convince.

Wielding a Bible and quoting the New Testament, the preacher pontificates, but does not act. And, while making Ribeiro's point that it is easy to believe in God when you are not sure about yourself (Anthony Attah certainly lacks conviction in the role), there's the rub with the plot.

When Matt Ian Kelly's rather tragic clown lies wounded on the tiled floor, the preacher simply cradles him in his arms, making verbal assurances that everything will be OK. He displays anxiety that wouldn't look misplaced outside a maternity ward, and wails for someone to get help, but (and perhaps this is down to the preacher in him) never follows the prescribed course of action himself. He bashes his fist against a cubicle in frustration. And, for a brief while, we share in his angst.

To 26 July (020-7701 0100)