Remarkably well-developed characters make “Dirty Pretty Things” seem too literary to be a… Remarkably well-developed characters make “Dirty Pretty Things” seem too literary to be a thriller. The depravity they encounter makes it seem too dark to be a thriller. Technically, though, it is one. Writer Steve Knight’s hook: The film’s protagonists are exploited illegal immigrants in London. They might as well be in hell.

Okwe (Chiwetel Ejiofor), a doctor before he emigrated from Nigeria, is a taxi driver by day and hotel desk clerk by night. He’s surviving, but at a cost: He never sleeps. He won’t let his guard down; his existence in London is too fragile. He shares an apartment with paranoid Turkish immigrant Senay (Audrey Tautou), who is a maid at the hotel in secret – her foreign national status forbids her to work.

The film’s plot takes shape when Okwe finds a human heart clogging the toilet in one of the hotel’s rooms. His manager (Sergi Lopez), suspiciously unsurprised by the find, tells him to forget it – this sort of thing is part of the hotel business. But Okwe can’t forget. And for fear of his illegal status coming to light, he can’t deal with the police either. He has to uncover the hotel’s dirty little secret on his own.

Ejiofor is a welcome new face, completely believable as a complex leading man – Okwe comes across as able and intelligent, but also strung-out and desperate. Tautou does some nice breaking down; if you fell in love with her as the title character of “Amelie,” prepare to be devastated by her fate here. The quasi-romance between Okwe and Senay adds an extra layer of sadness to their trip through the wringer. And Lopez, as a devil whose proposition poses the film’s central moral question, is perfectly hateable.

Director Stephen Frears, who’s been successful in multiple genres over the past two decades (dramas like “Dangerous Liaisons” and comedies like “High Fidelity”), is back to the kind of well-drawn characters and dark subject matter he portrayed in one of his best films, 1990’s “The Grifters.” It’s just too bad he doesn’t have as good an ending this time around. The resolution of “Dirty Pretty Things” lacks the edge present in the rest of the film.

Still, it’s a solid, intellectual thriller. And more than worthwhile.

“Dirty Pretty Things” opens August 29 at The Oaks Theater, located at 310 Allegheny River Boulevard in Oakmont. Call (412) 828-6311 or visit www.theoakstheater.com for more information.