THEATRE / Another piece of the puzzle: Paul Taylor on David Mamet's The Cryptogram, with Lindsay Duncan and the comedian Eddie Izzard

Oleanna was renowned for arousing rancorous controversy. 'If you don't see it, you can't argue about it,' the advertisement ran. The Cryptogram, David Mamet's well-named latest play, is likely to have the opposite effect: if you don't see it, you can't share in the togetherness of mass perplexity. It's a compressed, painful, tantalising piece, and not just because it leaves you feeling that your clumsy fingers have never quite grasped its key.

Fifteen years in gestation, this short three-hander gives off a strong sense of being the kind of work in which the author is trying to externalise and come to terms with some deep childhood trauma. As often happens in such cases, though, the line between what possesses profound private meaning for the writer and what he has succeeded in objectifying on stage seems to have grown fuzzy. In that regard, The Cryptogram ironically mirrors the predicament of John, its 11-year-old protagonist. Unable to sleep and under great stress because of family upheavals, he begins to hear voices and to misjudge the overlap between his haunted dream world and his actual life.

The play is set in Chicago in 1959, although so little is made of either the place or the period that this specification would appear to be just a further pointer to autobiographical origins. As it opens, John, played by the excellent Danny Worters, an intense little boy with a distinct look of Mamet, is anticipating a rites-of-passage camping trip in the woods with his father. From the moment, though, that he starts to nag about staying up until his father comes home, you suspect not only that the trip will fail to come off, but that the father will fail to come home.

This is just the first of a series of betrayals that are brought to light or are provoked during the course of the drama. Like Mamet's first big success, American Buffalo (1975), The Cryptogram involves a parent, a child-figure, a friend and impending treachery. In the earlier play, a junk store owner is persuaded, against his better judgement, to turn on his young, insecure protege by a flashy poker buddy who wants the boy's piece of the action in a planned robbery. The climax of The Cryptogram, likewise, comes when the mother is incited to sudden and swingeing verbal violence against her son. She, too, is betrayed into betrayal, but the new play arrives at this point very differently, owing to the nature and relationship of the two adults.

The family friend here is the homosexual Del, whose repressed in-period queeniness (all tweed jackets and bow ties) and whose drolly responsible manner towards the boy is beautifully captured by Eddie Izzard. The one man whom Donny, the mother, can rely on? Well, no, for it tragicomically emerges that Del, a lonely figure who lives in a hotel, has betrayed their long friendship by complicity in the husband's infidelity, and is also guilty of allowing John to live in false hopes of the treasured trip. The irony is that it's her child who becomes the scapegoat for all this male treachery. When he breaks a promise about staying upstairs and going to sleep, something snaps in Lindsay Duncan's superbly acted, tender but ground-down, maternal but patience- frayed mother. He cops it for the broken promises of the entire sex.

Although it should lose the disastrous and unnecessary interval after the first scene, Gregory Mosher's fine production is keenly sensitive to the rhythm of the piece - accumulative tension played off against the comedy of repeated anticlimaxes, as whistling kettles, say, or sudden losses of invention, distract people from making the overwhelming statement. The cast copes wonderfully with Mamet's fractured, groping, camouflaging dialogue, performing on a set by Bob Crowley which, with its vast staircase and nightmare-dark walls, shows you the house from the boy's overwrought, incipiently pubertal perspective.

Where the code of The Cryptogram is hardest to crack is in its tight constellation of charged objects and duplicitous symbols. Referred to on several occasions is a photograph of times gone by, in which Del may or may not be wearing the husband's shirt. What does this insinuate, if anything, about a relationship that is otherwise left extremely hazy? And what about the husband's German combat knife, the (alleged) reward to Del for his complicity, which turns out to have been a purchase, not a real trophy of war, and is thus farcically devalued in sentimental terms. An ambiguous emblem of deception and of cutting yourself free, it winds up in the hands of the boy - resulting in a final picture which, like much of the preceeding play, remains potently cryptic.

At the Ambassadors Theatre, London WC2. Box office: 071-836 6111

(Photograph omitted)