Treats was despised, derided and written off by critics at its 1976 Royal Court premiere as an "arid, barren, dreary waste". How wrong those reviewers were!

This chilling, black comedy of sexual manners by Christopher Hampton deals with far more than the eternal triangle of two middle-class chaps coming to grief and violence over the body of a sexy girl.

Laurence Boswell's production makes the problem as clear as a psychotherapist's court report, thanks to the power with which Billie Piper, in an impressive West End debut of genuine emotional power, and dynamic Kris Marshall, together with Laurence Fox's over-doltish man in the middle, act out their love-relations.

Treats spotlights a life dilemma: what happens when you are locked into the pains and insecure pleasures of a sado-masochistic relationship.

Hampton explains that Treats inverted the famous process of Ibsen's The Doll's House, where the heroine walks out on her controlling husband. Instead he considers the problems posed when a girl comes back to her man.

Hampton has not, I deduce, done any serious rewriting, aside from changing the odd reference, but the language sounds distinctly Seventies formal, while Jeremy Herbert's design offers a mystifying mix of objects from the Seventies and 2007: a typewriter jostles with CDs, DVDs, a flat screen TV and a computer.

Wherever we are, though, a timeless pattern of sexual behaviour is at once elaborated.

Marshall's international reporter, an outrageous sociopath called Dave, shatters a window and breaks into the life of his former lover, Piper's demure Ann, who lives now with Fox's dull, weedy Patrick.

Not content with knocking Patrick to the ground, Dave, who displays the seductive potency of a charming, self-centred adolescent, tearfully attempts to reclaim Ann, as if she were a cherished piece of luggage left too long in Lost Property. In a sense she is.

The charismatic Marshall, a natural actor right down to his toe nails, draws the comic maximum from Dave's shamelessness and revels in the man's unspeakable egotism, while Fox's Patrick looks on in dumb-founded, long-suffering passivity.

Piper's voluptuous Ann, exuding a fine contempt and distaste for this intruder, accuses Dave of having bullied and terrorised her, not to mention sleeping with some 42 women while with her.

"When I look at the marriages of my friends all I can see is easy pickings," he explains in witty justification.

Women who love too much will recognise the repartee: the accusation and cruel, insouciant response. A history of masochistic suffering and sadistic dominance becomes apparent.

Up to the interval, though, Treats rates as a superficial and trivial comedy of manners, whose three characters are mere types and never given professional identities or detailed personalities.

Hampton has, though, prepared his ground with psychological astuteness for the devastating second act.

Ann, true to her masochistic promptings succumbs to Dave. "Why do you treat me so badly," she asks. "Why do you let me" he counters, confessing he thought it was what she wanted.

Poised to resume their sexual relationship, he lands a blow upon her and walks out, his control asserted and soon achieved.

Ann, who rains down contempt upon the spurned, surely masochistic Patrick, does return to Dave, who is last seen raising a hand to prevent her from coming close. They are set for a wretched marriage.

Treats enthralls, with its convincing demonstration of how sado-masochists have little long-term fun.