Neil LaBute says that his play is about relationships rather than the politics of terrorism. But, while it is perfectly legitimate to use the events of September 11 to examine unheroic individual lives, The Mercy Seat rests on a series of artificial moral dilemmas.
In itself, the basic situation is ingenious. Ben is a married man who has been having a clandestine affair with his unwed, fortysomething employer, Abby. But instead of being, as scheduled, at the World Trade Centre on the morning of September 11 2001, he was in her apartment enjoying sex.
A day later they are still in her flat. The big question is whether they should take advantage of his assumed "death" in the catastrophe to run off and begin a new unfettered existence. LaBute is right to point out that our response to national disasters is often selfishly inappropriate. But the dilemma faced by Abby and Ben would only make sense if they were sexual, emotional and intellectual equals.
On the evidence presented here, however, she is an intelligent woman while he is a gutless jerk. And it is hard to believe that she would sacrifice career, apartment and cosily affluent life for a man who has never once looked her in the eyes during the act of lovemaking.
What LaBute is good at, though, is capturing that frayed bitterness of a flagging relationship where every word becomes a potential minefield. The generational difference is also well caught by Abby's irritation at Ben's ignorance of her random references to Audie Murphy and Guy Burgess.
But the more successfully LaBute evokes a terminally exhausted relationship, the more rigged the central dilemma appears. By the climax you feel LaBute is simply using 9/11 as a convenient device to dignify an end-of-the-affair play.
The one thing that kept me rivetted was Sinead Cusack's performance as Abby. She has an astonishing capacity to switch from blistering irony and merciless honesty to rueful regret and erotic tenderness in a second; and it is no fault of hers that you never feel Abby is really dining in the last-chance sexual saloon.
John Hannah does all he can to make you warm to the flabbily parasitic Ben, and Michael Attenborough steers the actors skilfully around Robert Jones's furniture.
But this is a play where you feel the really big issue is the one that is happening offstage.
· Until December 6. Box office: 020-7359 4404.
