The prime reason for reviving this distinctly minor David Mamet play must be Kim Cattrall's eagerness to appear in it. Her decision to do so seems even stranger than The Cryptogram itself.

For her conventional role as Donny, a 1959 wife and mother in Chicago, suffering from severe husband trouble, runs a poor second to that of her unhappy, disturbed 10-year-old son, John (Oliver Coopersmith) in Josie Rourke's production.

John's experience, judging from Mamet's autobiographical essay in the programme, owes something to the playwright's own childhood. So, unsurprisingly, as the victim of his parents' break-up John takes the lion's share of Mamet's oblique compassion. Coopersmith does not altogether act the obstinately radiant Cattrall off the stage.

He becomes the inevitable focus of sympathetic attention when on it. The handsome star maintains her look of winsome, unruffled composure and elegance even when convincingly tearful or after Donny loses both temper and husband. I dare say it's all very Fifties middle-class American housewife.

A cryptogram is something written-in cipher, requiring a key. Yet for all the air of mystique that foggily swirls around the play there is no disguising its blatant, melodramatic underpinning. In three scenes and 65 minutes Mamet advances from scenes of comfortable domesticity to fury, tears and delusions.

At first, though, tranquillity reigns and boringly so. Insomniac John, who is due to go camping with his father the next day, sits on the sofa with his mother's geeky, best friend, Del. Douglas Henshall makes a good, drab geek, with his look of chronic meekness and sexless regard for Donny.

Something, though, is already interestingly afoot. We are warned disasters come in clusters of three. John keeps climbingand descending designer Peter McKintosh's ominously steep, significantly numerous stairs to the bed where he cannot sleep and hears singing and voices.

In the living room, en route to bed again, he chances upon that antique, outmoded device, the sealed letter that noone has noticed or bothered to read. It contains a note from Donny's husband that leaves her shocked and amazed.

Mamet, who has maintained an uncharacteristically slack dramatic mood, then begins to notch up the tension as the whereabouts of a camping knife given to Del by Donny's husband assumes crucial importance. Could it be that Del has in fact been acting as the adulterous husband's cover and why?

Del's sexually tinged confession, that breaks his friendship with Donny, sound unbelievably contrived. It is revealed in the language of TV soap opera and come complete with such clichés as "Are you blind," "You don't want to know," and "Me, the poor geek."

Yet there is still the son, dimly, anxiously aware of catastrophe and dissolution, the innocent victim who hears voices, deluged by Cattrall's dangerous torrents of misdirected invective.

Coopersmith's uncomplaining John stands in silence, fearful of voices in his head. He conveys in a devastatingly restrained performance to what grief comfortable middle-class childhoods may be led.