After Kate (Potente) falls asleep waiting for the last train at the Charing Cross Tube station, she wakes up to find herself locked inside the Underground. An encounter with a slimy womaniser (Sheffield) freaks her out, so she takes refuge with a homeless couple (Rattray and Scott) and eventually a sewer worker (Blackwood). Together they must try to escape an unseen presence (Harris) who's violently killing the station's sparse overnight population one by one.

For most of the film, Smith adeptly avoids cliches with smart writing and inventive direction. The film feels organic--this is the way real people behave in these kinds of situations, although as the story progresses they begin to do stupid things like, well, I'm not telling. Meanwhile, Smith shoots the film cleverly, playing with focus and depth of field to overcome his budget limitations and make the setting look both eerily familiar and terrifying at the same time.

Potente seems a bit miscast here, but handles it well, as do the rest of the actors, although Harris' "creep" is rather goofy, really. But by the time we see him the film has us in its grip with its relentless pacing and knowing script. There are, of course, overtones of Phantom of the Opera here, as well as a playful infestation of rats and several astute comments on homelessness.

But Smith is going for the fright factor, and he gets a bit carried away at times. There are at least two scenes of gratuitous gore that add nothing at all to the narrative. And when the film goes silly at the end, it goes very silly indeed, with little coincidences and unlikely bits of horror-movie business that undermine the clever logic of the film's first two-thirds. But the extremely witty final scene will leave you throwing quick glances into the corners for quite awhile after the lights come up.