“We are the people you don’t see. We drive your cabs, clean your rooms and suck your c—s.” – Chiwetel Ejiofor, “Dirty Pretty Things.”

Stephen Frear’s newest work, thriller “Dirty Pretty Things,” is ostensibly about a conspiracy of organ harvesting, yet it is in fact the tale of much more. It’s a drama about the ruthless underbelly of a big city that few ever see. That’s the world of immigrants both illegal and barely legal, the shadows of people that we barely notice, but whose hard-luck lives may just be what keep the city running and the society moving smoothly.

“Dirty Pretty Things” is set in the gritty, dead-end alleys of London, far from the view of Big Ben and Buckingham Palace. It’s the tale of harsh, dead-end lives, and the desperate folks who are, and must be, willing to do anything to survive.

The action centers around the tiny Baltic Motel, and African night clerk Okwe (British stage actor Chiwetel Ejiofor) an illegal alien, a doctor in his former country who now barely makes a living working two jobs: His after hours gig at the Baltic and his day job driving taxis through London. He chews an herb to keep him awake, and has a crush on Senay (“Amelie” gamine Audrey Tautou, speaking English with a middle eastern accent) the Turkish maid whose couch he rents.

Senay is in London on a visa, but she’s not allowed to work; Okwe isn’t even supposed to be in the country. When he finds a human heart clogging the toilets in the room a mysterious, flirtatious hooker has just left, Okwe is left in the precarious position of either going to police, but risking jail and deportation, or letting a possible murder slip through the cracks.

“Dirty Pretty Things” is slow-simmering thriller, the kind of old-fashioned mystery that relies more on the interactions of the characters rather than big plot twists that do nothing more than contort the movie into a knot. Its main concern is not, in fact, thrills; it is the explorations of the lives of these characters, and the struggles they endure.

“Dirty Pretty Things” is at its best when it focuses on the relationship between Senay and Okwe; it’s obvious that both of them like each other, yet Okwe’s loyalty to his wife keeps him from making a move on the wide-eyed beauty. Okwe becomes protective of Senay, especially after she leaves the hotel to work at a sweatshop, where she is used by the shop’s oily owner. Senay, in turn, grows steadily more attracted to the handsome and dignified Okwe.

The thriller element is a contrivance, but Frears makes it a compelling one. The twists – or what pass for twists – aren’t all that surprising, but Frears and writer Stephen Knight (creator of “Who Wants To Be A Millionaire?”) still make the mystery riveting to watch, balancing the darkness of the material with sharp moments of humor and sweetness. Though Tautou is capable as the tremulous and damaged Senay, “Dirty Pretty Things” is grounded by the central performance of Ejiofor. It is he who makes the movie entrancing to watch. His sturdy and regal performance constitutes what leading men are made of. He’s graceful and decorous, and acts with a kind of intelligence, an emotional force rarely seen in Hollywood thrillers.