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…

Promising fund manager Jae-hoon is at the brink of losing everything when his company goes bankrupt. Overwhelmed by despair, he takes an impulsive trip to Australia where his wife and son live. As his trip nears its unexpected end, Jae-hoon gets a chance to look back on his life.