A group of tired commuters h**e caught the last train home, ready to hop into their *eds for the night. However, their train soon veers off-co**se and crashes into an a*andoned tunnel. The three s**viving commuters; withdrawn mother Yi Ling, her son Lucas, and student Jan***, are forced to *and together and s**vive the night, as well as **oid the mysterious monster hunting them. Yi Ling still suffers from flash*acks to the car accident that killed her hu**and and nearly took Lucas` life too. When Lucas is snatched away *y the monster, her maternal instincts are ****ed, and Jan***`s ideas of family are challenged as she remem*ers her difficult relationship with her estranged father. *ack at the su*way control headquarters, the engineers do their *est to make sense of the situation and rescue the s**vivors.