Ladies, if you have a teenage daughter who is the spitting image of the way you once were, guard against letting any of your old boyfriends back into your life, however fondly you cherish those dim memories of adolescent fumbles together. Kevin Elyot's new play, Forty Winks, reveals the dire consequences of Don's decision to look up Diana many years after they groped, as school chums, in the darkened stalls of the Continental cinema. The passage of time has been long enough for Diana to have fallen in and out of love with her husband, Howard, and to have lost her looks, too. But the enticing beauty that used to be hers has been reborn in the 14-year-old Hermia, and it entices still.

Elyot's play is a masterpiece of concision. In an hour and ten minutes, which includes the awkward pauses you would expect when people meet again after so long, he presents us with a lexicon of human misery. A few words suffice to denote the yearning felt by each character. By their early thirties, they all live in despair, regretting the decisions they have made, yet refusing to accept the duff hand that fate has dealt them. Don's arrival blows away the cover of normality under which they hide their unhappiness.

With so few words to say, the characters inevitably remain sketchy. Two of them spend much of the play asleep. One dies before the end. The director, Katie Mitchell, emphasises that the characters are mere silhouettes by having her actors frequently speak (and perfectly audibly) standing with their backs to the audience.

We first discover Don (played by Dominic Rowan) in a cheap hotel room. There is nothing attractive about him. He is a man of few words. A paunch is developing already. His life has been spent wandering, but he has made nothing of his chances despite having tried his hand at many things. Yet we find him with his shirt unbuttoned and drenched in sweat, suggesting that he has been interrupted while having sex. Or maybe his jumpiness indicates that his secret is something worse. That much is clear, even before Diana (Anastasia Hille), herself a bag of nerves, arrives with the intention of throwing herself at him, hoping to recapture what they experienced years earlier under the flickering beam of the cinema projector.

In fact, nearly everyone wants sex with Don. Goodness knows why. He is wholly lacking in charm or grace, dogged by a persecution complex, stuck in a reverie of pubescence, and by the play's end he appears plain sinister. But neither girls nor boys can resist him.

There is one outsider, Danny (Stephen Kennedy), who senses something evil about the emotionally crippled Don. Danny probes why he has returned, and why he wants to strip away the veneer of calm from the folk he has not seen for 15 years. Howard (Simon Wilson) is also able to resist Don. Indeed, he heartily dislikes him. It has been like that bet- ween them from their schooldays, when Howard not only snatched Diana from Don, but ruined his rival's reputation, too. Those are the scars that have disfigured Don's personality. The scandal in his youth brought shame on his parents, and in compensation he dotes hopelessly on his mother. This was bad enough while she was alive, but now it has become macabre. He carries her ashes around in a plastic bag.

Don has an excellent speech about his Oedipal condition. He delivers it in his hotel room to the unconscious Hermia (Carey Mulligan), who is suffering a nar-coleptic attack. You may be beginning to understand the play's title. Written staccato fashion, Don's words provide a brilliantly terse piece of self-pity and self-justification, a memorable excuse for lust and crime. Such moments demonstrate the virtuosity of Elyot's writing. I did not always find the play credible, particularly the ending, but it is a splendid piece of composition.

Given that the characters are intended to be mere outlines, it would be wrong to criticise the actors for offering caricatures in their roles. Paul Ready as Howard's younger brother Charlie is remarkably effective with a simple repeated gesture of slapping his hand protectively against his chest. Maybe Hille overdid the panting nervousness that accompanies Diana's rekindled hopes of sexual adventure. Rowan resisted the temptation to make his character too interesting. Rightly, he ran the gamut of emotions from A to B.

It will not be obvious from this description that the play has many hilarious moments. Elyot spies humour glinting from the darkest crevices of human suffering and the actors timed the gags beautifully. The obscenities are so shocking that laughter seems the only adequate response.

Nevertheless, it could have been better. Elyot deals with the shocking subject of paedophilia, but the impact is blunted because the plot is implausible. This saves us from feeling too shocked. Elyot has copped out, and that is a pity, because Forty Winks has the makings of a really disturbing evening.

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