In a world where an app alerts people if someone in the vicinity likes them, Kim Jojo experiences young love while coping with personal adversities.

The Subway Police of Wangsoori Station is led by Chief Inspector Ko Ji Seok. He is the best of the best, although his only goal in life is to have a stable, uneventful career. However, a serial killer, nicknamed "the Subway Ghost", strikes the Subway Police 30 Year Anniversary event. An applicant shows up for a job interview to join the team.

In a mythical land called Arth, the inhabitants of the ancient city of Arthdal and its surrounding regions vie for power as they build a new society.