When a shocking mass shooting shatters Korea's calm, Lee Do races to stop the violence — then realizes the threat of illegal guns is just beginning.

Guns reach bullied students and grieving parents, sparking new tragedies. Lee Do uncovers a network delivering weapons to vulnerable people across Korea.

Police raid the gun syndicate, and rival gangs and old enemies clash in bloody battles. Lee Do is pushed to the limits as violence hits all of Korea.