London, midnight, on a cold evening. Unable to find a taxi, Kate (Franka Potente) heads for the Underground. She takes a seat away from the crowd of late-night revellers and waits for the last train. Before long she drifts off to sleep… and wakes to find everyone gone. She momentarily panics until another train pulls in. She boards, unnerved that she's the only passenger, but relieved at last to be on her way. Halfway through the tunnel the train jerks to a violent halt. The lights shut off and the train is plunged into darkness. Kate screams… she is trapped, in the dark… and she is not alone… her nightmare has only just begun.