A group of tired muters have caught the last train home, ready to hop into their beds for the night. However, their train soon veers off-urse and crashes into an abandoned tunnel. The three surviving muters; withdrawn mother Yi Ling, her son Lucas, and student Janice, are forced to band together and survive the night, as well as avoid the mysterious monster hunting them. Yi Ling still suffers from flashbacks to the car aident that killed her husband and nearly took Lucas` life too. When Lucas is snatched away by the monster, her maternal instincts are tested, and Janice`s ideas of family are challenged as she remembers her difflt relationship with her estranged father. Back at the subway ntrol headquers, the engineers do their best to make sense of the situation and rescue the survivors.