Stephen Frears' "Dirty Pretty Things" is, like its title, a study in contrasts. It's both a love story and a horror story. Its characters are, at heart, stereotypes, but somehow manage to be convincing, three-dimensional human beings. It's written and produced by the team that co-created "Who Wants to Be a Millionaire," but is nevertheless one of the year's most literate and thoughtful movies.

Set in modern-day London, the movie follows the lives of the anonymous immigrants who populate the service industry, driving the city's cabs, cleaning visitors' hotel rooms, servicing traveling businessmen's sexual needs. It's a brutal, uncompromising film and yet (another contrast) the filmmakers never become preachy or heavy-handed in their treatment of its serious issues. In fact, the movie sometimes isn't serious at all - Frears and screenwriter Steven Knight fill "Things" with a black humor that can be comically - and invaluably - distracting at times.

Most of the movie's action takes place at a midlevel London hotel, which Frears transforms into a ring of Dante's Inferno. The hotel is run by displaced foreigners, most of whom are in London illegally. These people are barely getting by, trying to keep a roof over their heads, food in their stomachs and the law off their trail. Essentially, these people live in a prison, ignored by the general populace and acknowledged only by the police who want to deport them.

The main character is Nigerian-born Okwe (Chiwetel Ejiofor in a brilliant turn), who drives a cab by day and works the night shift at the hotel's front desk. Okwe comes to discover that his boss, Sneaky (Sergi Lopez, the psycho in "With a Friend Like Harry"), is exploiting the immigrants' desperation in a black-market operation that's straight out of some nightmarish urban legend. If Okwe lends a hand, he might better his life - and that of fellow immigrant Senay ("Amelie's" Audrey Tautou) - but lose his soul in the process.

"Dirty Pretty Things" is this month's second film to render London in a way we've never quite seen. Whereas "28 Days Later" memorably gave us glimpses of a sleeping city abandoned to death and despair, Frears and master cinematographer Chris Menges ("The Killing Fields," "The Good Thief") offer another variant of chilly inhospitality that welcomes its immigrants in the same manner that Stalingrad opened its arms to the Nazis in the winter of 1942.

It's just one accomplished facet of a film that does so many things well. Thriller, romance, caper movie, black comedy - "Dirty Pretty Things" is all these things and more, hard to synopsize, harder still to forget.