Cho Eun-ji

Honed from childhood into a merciless killing machine by a criminal organization, assassin Sook-hee is recruited with the promise of freedom after ten years of service. However, secrets from her past destroy everything she’s worked for and now she embarks on a roaring rampage of revenge.

At the same time as murder suspect Yeo-hoon is brought unconscious to the emergency room following a shooting incident, an assailant breaks into the house of Tae-jun, the emergency room's doctor in charge, and kidnaps his wife. The kidnapper calls the doctor and tells him to bring Yeo-hoon to him. To retrieve his wife, Tae-jun has no option but to save the patient and sneak him away before the police can notice.

A serial killer reappears 15 years after his murder spree with a book detailing his crimes. The resentful cop who failed to catch him before is assigned to protect him. The families of the victims plan revenge. And as the media circus spirals out of control, a masked man called "J" appears claiming to be the real killer.