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.

As shootings spread, Lee Do discovers guns in the hands of everyday citizens. When a victim hits close to home, his investigation grows more urgent.

A police raid uncovers a cache of military weapons. Lee Do and his new ally Moon Baek close in on the arms network as the city reels from bloodshed.

Lee Do confronts a violent standoff and must decide how far to go to stop the killings, while suspicions about Moon Baek threaten their fragile alliance.

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

A gun in the hands of a student spells crisis at school. As panic spreads, Lee Do and Moon Baek race rush to restore order — but it may be too late.

As fear and confusion grow, police and gangs rush to recover illegal guns. Lee Do feels powerless as the true scale of the arms crisis comes to light.

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.