A young man is on his way to work in the subway during rush hour. He gets a call from his ex-girlfriend, and while he's talking to her, he realizes that he's lost in the subway tunnels and can't find his way out. The young man is forced to walk the same route until he meets certain conditions eight times in a row: if he notices an anomaly, he must turn back, and if nothing changes in the tunnel, he must continue walking.