By day, So Ji-sub plays Kim Do-hyeon, a quiet bank manager and devoted single father trying to raise his teenage daughter while leaving his troubled past behind. To everyone around him, he is an ordinary office worker living an unremarkable life.
But Kim Do-hyeon is hiding a dangerous secret: he was once an elite black-ops operative and one of the most feared agents in the Korean peninsula. When his daughter Min-ji suddenly disappears without a trace, the peaceful life he built begins to crumble.
With the police making little progress and time running out, the former agent is forced to awaken the deadly skills he buried years ago. As he follows the trail of his daughter's disappearance, he uncovers a web of corruption, powerful enemies, and secrets that threaten not only his family but everyone around him.
Driven by desperation and a father's love, Kim Do-hyeon becomes Agent Kim once again — willing to cross any line and destroy anyone standing between him and his daughter. Alongside two old comrades who are now fellow fathers living ordinary lives, he launches a relentless rescue mission that blends brutal action, emotional stakes, and themes of family and sacrifice.