Unable to find a taxi in London, Kate (Franka Potente) heads underground. Waiting for the last subway train, she dozes off and awakens to find everyone else gone. Gripped by panic, Kate realizes she's locked in - but she's not alone. Lurking in the pitch-black maze is something unimaginable. Something that calls a deranged laboratory home. And something that's determined to make this subterranean hell Kate's last stop.