Agroupoftiredcommutershavecaughtthelasttrainhome, readytohopintotheirbedsforthenight.However, theirtrainsoonveersoff-courseandcrashesintoanabandonedtunnel.Thethreesurvivingcommuters;withdrawnmotherYiLing, hersonLucas, andstudentJanice, areforcedtobandtogetherandsurvivethenight, aswellasavoidthemysteriousmonsterhuntingthem.YiLingstillsuffersfromflashbackstothecaraccidentthatkilledherhusbandandnearlytookLucas`lifetoo.WhenLucasissnatchedawaybythemonster, hermaternalinstinctsaretested, andJanice`sideasoffamilyarechallengedassheremembersherdifficultrelationshipwithherestrangedfather.Backatthesubwaycontrolheadquarters, theengineersdotheirbesttomakesenseofthesituationandrescuethesurvivors.