Legion focuses on David Haller, 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 met and fell in love with a beautiful and troubled fellow patient named Syd. After a startling encounter with her, he was forced to confront the shocking possibility that the voices he hears and the visions he sees may actually be real. With the help of Syd and a team of specialists who also possess unique and extraordinary gifts, David unlocked a deeply suppressed truth: he had been haunted his entire life by a malicious parasite of unimaginable power.