Journalist Sang-jin uncovers the existence of the so-called ‘Troll Factory’ while investigating an online public sentiment manipulation story, and is confronted with an unbelievable truth.

On a Christmas Eve, a lifeless body of teenage boy is found. The victim’s revenge-driven twin brother checks himself into a juvie to hunt down the suspects.

Ji-woo, an outcast at a prestigious private school, meets Hak-sung, the school janitor who is actually a mathematical genius who defected from North Korea.