William Saint is dying of cancer. On most days death seems like a humane alternative to the treatment. Stricken with fever, William is rushed to Mercy—notorious as a place to send the sickest of the poor and uninsured to be forgotten—and finds the hospital in even worse condition than his previous visit. The grounds are unkempt, the foundation is cracking, and like the wild mushrooms sprouting from fissures of decay around it, something is growing inside the hospital. Something dark. It’s feeding on the sickness and sustaining itself on the staff, changing them. And now it wants Willie.