David Haller is a troubled young man who was diagnosed with schizophrenia as a child. Shuffled from one psychiatric institution to the next, in his early 30s, David meets and falls in love with a beautiful and troubled fellow patient named Syd. After a startling encounter with her, he must confront the shocking possibility that the voices he hears and the visions he sees may actually be real. Syd leads David to Melanie Bird, a demanding but nurturing therapist who heads a team of specialists -- Ptonomy, Kerry, and Cary -- each of whom possesses a unique and extraordinary gift. Together, they help David to recognize and harness his hidden abilities and unlock a deeply suppressed truth -- he has been haunted his entire life by a malicious parasite of unimaginable power.