One plague seems to be the cause of death for many, and those who live with it find the doors of their houses marked with a large red X painted there by the military. Although there is a cure, many do not receive it as it is very expensive. There is also medicine to suppress the disease, so that the sick may recover. Day fights to keep his family fed and free of the disease, all while staying out of notice of the military. In the beginning of the book, the plague is found only in 4 districts, but later spreads to other districts. It is unknown how the plague spreads.