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