Bad Boy Bubby is just that: a bad boy. So bad, in fact, that his mother has kept him locked in their house for his entire thirty years, convincing him that the air outside is poisonous. After a visit from his estranged father, circumstances force Bubby into the waiting world, a place which is just as unusual to him as he is to the world.

When a zombie virus pushes Korea into a state of emergency, those trapped on an express train to Busan must fight for their own survival.