The book narrates Cahalan's issues with anti-NMDA receptor encephalitis and the process by which she was diagnosed with this form of encephalitis. She wakes up in a hospital with no memory of the events of the previous month, during which time she would have violent episodes and delusions. Her eventual diagnosis is made more difficult by various physicians misdiagnosing her with several theories such as "partying too much" and schizoaffective disorder.

The book also covers Cahalan's life after her recovery, including her reactions to watching videotapes of her psychotic episodes while in the hospital.