It's London, midnight, and the city is enduring the worse rainfall in a century. Unable to find a taxi to take her to her next party Kate, heads for the London underground. She buys a ticket from a homeless girl and descends to the platform where she soon falls asleep. She wakes to find herself completely alone and locked in, with no signal on her cell phone, monumentality panicked until the last train pulls in. She boards, unnerved that she'd 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.
A man with a torch appears in the adjoining car and moves swiftly towards her. As the figure approaches through the connecting doors, it becomes clear it's someone she knows from the party. But this momentary relief evaporates as he lunges for her and tries to force himself upon her. In a split second the carriage doors fly open and Kate's assailant is pulled off her by a shadowy figure and hauled backwards out of the train.
Blood curling screams fill the tunnel, then silence. Kate bolts through the train, hides in the driver's carriage, and listens. There is nothing, then dull footsteps, then a rasping breath. She jumps down onto the tracks and runs as fast and as far as she can.
But for Kate and the few people she meets along the way, the nightmare has only just begun.