After a traumatic event, a drug trafficker turns sides and conspires with a dangerously ambitious undercover police officer to bring down the mysterious kingpin of a major drug cartel.
Set in the late 1920s, The Age of Shadows follows the cat-and-mouse game that unfolds between a group of resistance fighters trying to bring in explosives from Shanghai to destroy key Japanese facilities in Seoul, and Japanese agents trying to stop them.
Saeyoung is a new employee who eventually stands against Leesun, her stubborn team leader. Leesun is upset by Saeyoung's behavior, but she soon learns about ominous stories about Saeyoung. As the stories about Saeyoung are revealed one after another, she becomes a source of fear to Leesun. Saeyoung's stalking-like bullying continues, and Leesun tries to run away from her.