It's London in this brave new world, but it could well be New York or Sydney or any city that draws desperate people seeking work or an escape from their pasts. Mass immigration is nothing new, of course, but the fracturing of economies, both globally and locally, and the relative ease and speed of international travel have changed the face of it, from one-way journeys toward assimilation and adopted citizenship to a cycling of arrival, work, and departure, either home or on to another, supposedly even better city and opportunity. And so there exists now in places like London and New York a constantly churning underclass of temporary workers, often in the country illegally, ripe for exploitation, paradoxically, partly because they are more sophisticated than the immigrants of the past -- they have a better idea of the good life they're missing out on in and are perhaps more willing to do what needs to be done to get it for themselves.

Enter Nigerian Okwe (Chiwetel Ejiofor: Amistad), who drives cabs during the day and works the front desk of a posh hotel at night. His friend Senay (Audrey Tautou: Amelie) works as a maid at the hotel and lets Okwe sleep on her couch, when he does sleep, though she zealously protects the secrecy of this roommate business -- a nice Turkish girl, she's a virgin and plans to stay that way, in actuality as well as in the realm of gossip, until she's married.

There's some speechifying in Steve Knight's script, about the nasty, necessary work that these needed yet unwelcome visitors do, the kind of stuff you'd expect from a drama about working-class immigrants. But director Stephen Frears counters that with a dryly apocalyptic depiction of London -- dark, dirty, crowded, peopled with unknowable characters like Juan (Sergi López: Jet Lag), the oily security chef at the hotel, or men-in-black immigration agents who appear from nowhere. Okwe and Senay just keep their heads down, he too sleep-deprived and she too wary to do anything else, until they stumble upon a secret that busts open their comprehension of how this underworld they live in works. And their discovery busts the movie open, too, into an unexpected new place: what started out as a character study is suddenly a thriller, a kind of low-key horror movie, alongside the sneaky SFness of it, too.

The "science" in the science fiction here is social, the confluence of economic disaster and mobile workers getting a tweak toward the more extreme in this London 20 minutes into the future -- though Okwe and Senay's discovery has a technological aspect to it, too. But it's more than that: Dirty Pretty Things feels like science fiction, like the characters are navigating a world slightly askew from our own, like their world is spinning slightly out of control and there's nothing to do but watch, for them or for us. Senay pines for an escape from this dreary London for New York, where she imagines all the trees have lights in them, but one can't help but suspect that in this dystopian world, New York would have its own dark secrets on a par with this London's.