Here's a possibly supernatural mystery for Mulder to investigate: how did his partner Scully get involved in What the Night Is For? Since the occasion marks the London stage debut of Gillian Anderson, the latest American star to be appearing in the West End, Mulder might also enquire what it is about lousy two-handers that seems to draw star actors like moths to flames, where instead of flying they tend to get their acting wings severely singed?

The last few years have produced any number of examples, from Donald Sutherland in Enigmatic Variations and David Warner in A Feast of Snails to the Comedy Theatre's most recent tenant, On an Average Day, with Woody Harrelson and Kyle MacLachlan. Now we have another less than average play at the Comedy, where laughter is hardly on the menu as it earnestly seeks to replay the re-ignited passion of two former flames.

Eleven years ago, Melinda Metz (Anderson) and Adam Penzius (Roger Allam) - she an aspiring poet (now a teacher), he a budding architect (now a successful one) - met in New York and had a passionate affair. But she was, and still is, unhappily married to Hugo, heir to a bicycle business and now running for the Senate; while he was, and still is, married to Jan.

Now, as they meet again in an anonymous hotel room - number 410, anonymously rendered on a revolving platform by designer Tim Hatley whose usual flair for visual invention seems to have deserted him - playwright Michael Weller chronicles a long, dark night of the soul for them, and creates an even longer one for us.

There's nothing much likeable or remotely compelling about these two self-obsessed creatures, or the everyday predicament they find themselves in: trying to sort out the unfinished business between them as they sport and parry, howl and whimper about what might have been, and what could still be.

Both Anderson and Allam are good sports in seeking to keep our attention with these two tedious people and their selfish concerns. As she registers a range of emotions from doleful deer and petulant pup to mad monkey, Anderson has poise and a certain polish, but in the end cannot save a character who can barely save herself. Allam is solid support, but is dullish where he should be dashing.

Weller has the temerity in a programme feature to compare his very minor league work to David Hare's far more bracing play about former lovers, Skylight, and says he was struck by "how differently British people would deal with an encounter after years apart". Whereas Hare's characters "were talking very much about circumstance rather than the movements of their hearts," he goes on that he "wanted to write a play which would be much more focussed on the emotions involved".

But it's because Hare provided a wider context to his characters' lives that addressed their place in the world, not just this room, that his play lived - whereas this one, with its morbid introspection, barely comes to life.

- Mark Shenton