Trying to explain the meaning of Martin Crimp's new play is rather like groping through a maze on a foggy autumn afternoon as twilight falls. It's a process that intrigues and mystifies, irritates and engrosses.

At first it looks as if The City is set in familiar terrain. Here is a middle-class couple, Benedict Cumberbatch's Chris and Hattie Morahan's emotionally vehement Clair, a translator, arriving home to meet across the kitchen table and exchange pleasantries. The fact that designer Vicki Mortimer fills the stage with empty space, apart from a white table, wine glasses and futuristic, rectangular lights enclosed within the walls only engenders a hint of oddness.

In Crimp-land,however, nothing is what it seems. Alienation, streaks of black comedy and even apocalypse hover just around the corner, amplified by ominous sounds and allusions to hot weather.

While Cumberbatch's suitably deflated, pacific Chris has ordinary fears about being made redundant, Clair's account of being stopped by a man whose young daughter has just gone to live with his sister-in-law, a nurse, strikes strange notes. Why on earth does this chap, who turns out to be a famous writer called Mohamed, confide in Clair for two hours about being tortured in prison? Why does he give her a diary originally intended for his daughter to write down her thoughts?

Crimp, like Pirandello long before him, is fascinated by questions of identity, reality and theatrical form. So it's a fair guess that the increasingly weird scenes of this 80-minute play represent Clair's attempt to convert her fraught married life, with the now unemployed Chris, into a piece of imaginative fiction.

When another nurse - Amanda Hale as their nerve-prone, half-inaudible neighbour - arrives to tell an incoherent story of how her doctor-husband has witnessed the city they inhabit being pulverised and rent with barbaric violence, it sounds as if Clair's end-of-the-world fantasising is in full flood.

So it proves when Chris reads her diary and discovers that The City of the title represents the failed world of Clair's creative imagination in which nothing comes to interesting literary life. Mohamed, the nurse and even a musical child, are all failed creative sparks of fiction.

Katie Mitchell's fine production, exuding anxiety and tension, cannot disguise the fact that the inventive form of Crimp's play is more interesting than its loquacious content.

Until 7 June (020 7565 5000, www.royalcourttheatre.com).