In the 1980s, a zombie plague spreads worldwide and causes the deaths of an estimated 100 million people. An unprecedented amount of research goes into finding a cure, but the resulting medicine requires daily doses to be effective. If the infected miss even a single dose, they quickly and irrevocably degenerate to a feral zombie state. As the formula can only be extracted from dead feral zombies, there are constant rumors that the supplies will run out. Infected humans, called "the returned", are subject to discrimination and violence from bigoted and fearful uninfected humans.