Amid a royal and political power struggle, a king entangles with an intriguing woman — whose hidden desire for revenge transforms into unintended love.

A psychopath’s ruthless serial murders have left the entire nation gripped with fear and chaos. A honest and justice-seeking rookie police officer and a veteran detective with tragic past, face against the killer. After the encounter with the psychopath, their lives totally change.

Hyo-joo (Ha-neul Kim) is a temporary teacher at a boys' high school and Hae-yeong (In-yeong Yu) is a fellow teacher who is the school board chairman's daughter. One day, Hyo-joo witnesses Hae-young locked in a passionate embrace with a boy and she starts feeling an inexplicable sense of humiliation towards Hae-yeong.

Martial law is declared when a mysterious viral outbreak pushes Korea into a state of emergency. Those on an express train to Busan, a city that has successfully fended off the viral outbreak, must fight for their own survival…