A teenage boy, attired in a woman’s night-dress, a necklace and excessive lipstick, crouches by a bed on which his drunken mother sprawls. She is lost to the psycho-drama of her son, who is going out of his mind as surely as she has already gone from hers. His father and sister stand watching, like impassive spectators at a street accident. Voice, pitched screaming distress, limbs and nerves jangling, the boy rages, begs and accuses. Thanks to the award-winning author, 21-year-old Polly Stenham, and Matt Smith’s astonishing coup de theatre as the teenage Henry, guilty feelings are expressed with devastating impact.

This scene marks the climax and resolution of Miss Stenham’s That Face, premiered at the Royal Court, and which won her the Evening Standard’s Most Promising Playwright award last year. It generates such emotional power because it faces up unflinchingly to the consequences of a mother/son incestuous bond. This is the first play on the subject by an English author since Noel Coward’s more oblique treatment in The Vortex. It has the strange, uncomfortable ring of truth about it. Incest becomes the defining symptom of a rich, privileged, middle-class family in crisis and dysfunctional collapse.

The crisis is precipitated when Henry’s demure but under-characterised sister Mia (Hannah Murray) leads a school dormitory initiation ceremony, which with the aid of her mother’s pilfered Valium requires the victim’s hospitalisation. Julian Wadham’s bored, introverted father is called home from the Far East and a new marriage to deal with the family he would prefer to forget.

Although the dormitory incident beggars belief, betraying Stenham’s immaturity, she handles the incest theme with assurance. In Jeremy Herrin’s powerful, expressionistic production, a centre-stage bed is the single stage property. Here lies Henry’s mother, Lindsay Duncan’s Martha, a glazed alcoholic and blanched, petulant blonde, with something of several Tennessee Williams heroines about her.

In spellbinding scenes that steer a wavering line between black comedy and a drama of erotic possessiveness, the superlative, mocking Duncan, keeps Smith’s protective, guilt-laden Henry to heel and in bed, until he escapes for a first night with a girl. Martha’s jealous responses to her son’s bid for freedom, comic and dreadful, seal their fates. Matt Smith’s virtuoso performance makes it clear that Henry’s life rather than Martha’s has been ruined.

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