In a series of online posts, Parker H., a young psychiatrist, chronicles the harrowing account of his time working at a dreary mental hospital in New England. Through this internet message board, Parker hopes to communicate with the world his effort to cure one bewildering patient.

We learn, as Parker did on his first day at the hospital, of the facility's most difficult, profoundly dangerous case - a forty-year-old man who was originally admitted to the hospital at age six. This patient has no known diagnosis. His symptoms seem to evolve over time. Every person who has attempted to treat him has been driven to madness or suicide.

Desperate and fearful, the hospital's directors keep him strictly confined and allow minimal contact with staff for their own safety, convinced that releasing him would unleash catastrophe on the outside world. Parker, brilliant and overconfident, takes it upon himself to discover what ails this mystery patient and finally cure him. But from his first encounter with the mystery patient, things spiral out of control, and, facing a possibility beyond his wildest imaginings, Parker is forced to question everything he thought he knew.