Acoupleonthevergeofanastydivorceattempttoselltheiremptylovenestandmoveonwiththeirlives,separately.Afterasuccessfulopenhousetheyarehorrifiedtodiscover,dayslater,thatapotentialbuyerdidn'tleavetheirhome.WhileAliceisbeingheldcaptiveinthebasement,theunannouncedhouseguestmovesinupstairs.Shesenseshercaptureisbeingkeptarebellioussecret .Sheknowsherwayonlywayoutifshecanonlygetoutalive.