A group of tired commuters caught the last train home and prepared to jump into bed for the night. However, their train quickly veered off course and collided with an abandoned tunnel. Three surviving commuters; The lonely mother Yi Ling, her son Lucas, and student Janice were forced to unite and spend the night avoiding the mysterious monster chasing them. Yi Ling still remembers the car accident that caused her husband's death, and Lucas almost died. When Lucas was taken away by a monster, her maternal instincts were tested, and when Janice recalled her difficult relationship with her estranged father, her family values were challenged. Returning to the subway control headquarters, the engineers made every effort to understand the situation and rescue the survivors.