Can it really be true, or indeed fair, that the prolific and well-remunerated TV writer who brought us Who Wants To Be a Millionaire? has now come up with one of the tightest and most intelligent British films in ages? Well, it is true, anyway. Steven Knight's unusual script is an engrossing noir love story, couched in the language of both thriller and urban myth, brought to life with terrific zest and subtlety by director Stephen Frears. He works with three actors whom it is a joy to watch: Chiwetel Ejiofor, Audrey Tautou and Sergi Lopez.
Ejiofor plays Okwe, a Nigerian "illegal" working in London, hotel-portering by night, minicabbing by day, and all the time chewing dodgy herbal leaves to keep himself alert. Tautou is Senay, a young Turkish woman, also illegal, earning a pittance as a maid in the hotel where Okwe works. The incomparably sinister Sergi Lopez is the hotel manager. One morning, Okwe is brusquely instructed to clean up a room where a guest has been with a prostitute, and has to unblock a lavatory overflowing with blood - a gripping scene in which nausea gives way to astonishment, then fear as Okwe realises that the obstruction is caused by a human heart. When he challenges the manager, he is told only that London hotels are places where strangers come to keep secrets, and wise people look the other way.
From here, a creepy network of control opens out, which relies on keeping asylum seekers and immigrants - desperate for an EU passport, real or fake - in a state of mendicant servility and fear. Okwe and Senay have only each other to rely on; they begin the movie in a sweetly innocent brother and sister set-up, Okwe sleeping on her couch and infuriating Senay by running the hot tap in the kitchen while she is trying to take a bath ("Glasses need hot water!" - "So do women!"). Their relationship deepens into a gallant affaire de coeur as Okwe tries to protect Senay from the grisly forces that encircle them both.
Frears's movie has slightly broad elements of thriller in its final act, but it always keeps its drama on the right side of plausibility, if only by a whisker. With a toughly realist dimension reminiscent of Pawel Pawlikowski's Last Resort or Neil Jordan's Mona Lisa, it has things to say about how swinging 21st-century London is "multicultural" chiefly in exploiting immigrant labour for its service economy. Yet it manages also to be a very entertaining film into the bargain.
· At Odeon West End, London WC2, today at 3.30pm. Box office: 0870 5050 007.