Set in a Southeast Asian city, the story follows a group of commuters on the last subway train home, only to have the train veer off-course and crash into an abandoned tunnel. Stalked by an unknown monster, the remaining commuters - Yi Ling, a withdrawn mother guilt-ridden by her trauma in a car accident that killed her husband and nearly that of Lucas, her son, and Janice, a student dealing with an estranged relationship with her father - must escape and survive the night. When Lucas is taken by the monster, Yi Ling's maternal instinct is once again tested. Back in the subway control headquarters, duty engineers try to make sense of the situation and rescue the survivors, if there are any.