During a routine rush-hour commute, monstrous creatures attack a Seoul Metro Line 2 train, wreaking havoc and killing passengers. Among the survivors are three teenagers—sprinter Dan, streamer Yeona, and their friend Jitae—who attempt to escape, only to find all exits destroyed. As they navigate underground tunnels, they learn Dan’s mother is trapped at Noryangjin Station. Their mission shifts from survival to rescue. Can they save her before it’s too late?