The world in which immigrants live is one we often know little about. Stephen Frears' new film "Dirty Pretty Things" depicts the London underground of immigrants -- both legal and otherwise -- where doctors drive taxi cabs and hard-working women are forced to exchange sex for job security.

Okwe (Chiwetel Ejiofor) is a Nigerian immigrant, living and working in London illegally after he was forced to flee his homeland. Although he mines fares at Heathrow all day and works as the night porter in a hotel where hookers are regulars, he's trained as a doctor and the people around him often ask his medical advice.

Senay (Audrey Tautou of "Amelie") is a legal Turkish immigrant that works at the same hotel. She has a deal with Okwe. He can sleep on her sofa, but only when she's not there. She has nosy neighbors to contend with and when the immigration police start showing up looking for Okwe, her own future in the West is threatened.

Okwe wants to be able to go home, but Senay dreams of going to New York, where she has a relative and of which she harbors unrealistic expectations.

One night Okwe makes a disturbing find in one of the hotel rooms and the most thrilling and dramatic aspects of the 107-minute film spread from this discovery. But a an affection -- although a tempered one and a not unexpected one -- begins to blossom between Okwe and Senay and this subplot balances the film's mysterious aspects with its tender portrayal of two outsiders intersecting in a strange land.

The script, written by Steve Knight, a director and actor, is finely-tuned, and Frears does a masterful job as we've come to expect from the man behind "High Fidelity," "The Van," "Dangerous Liaisons," "Sammy and Rosie Get Laid," "My Beautiful Launderette" and others.

But the praise really must go to both Tautou and especially Ejiofor who step up with measured, emotional and driving performances. Tautou does an impressive job in what may be her first English role and certainly the first role where she must speak English with a Turkish accent.

The setting is London, but unlike other films, "Dirty Pretty Things" doesn't spend much time on footage of tourists riding through Piccadilly on red double-decker buses. Rather we see the sweatshops and the bustling high streets loaded with immigrant shops and we hear the music of the immigrants from Jamaica, the Middle East and elsewhere. Reggae fans especially will appreciate the use of a track by the late Garnet Silk in one of the film's early scenes.

"Dirty Pretty Things" opens Fri., Aug. 15 at Landmark's Downer Theatre.