Based on the Marvel Comics by Chris Claremont and Bill Sienkiewicz, LEGION is the story of David Haller (Dan Stevens), a man who believed himself to be schizophrenic only to discover that he is the most powerful mutant the world has ever seen. From childhood, David shuffled from one psychiatric institution to the next until, in his early 30s, he met and fell in love with a beautiful and troubled fellow patient named Syd Barrett (Rachel Keller). After Syd and David shared a startling encounter, he was forced to confront the shocking reality that the voices he hears and the visions he sees are actually real. With the help of Syd and a team of specialists who also possess unique and extraordinary gifts Ptonomy Wallace (Jeremie Harris), Kerry Loudermilk (Amber Midthunder) and Cary Loudermilk (Bill Irwin) David unlocked a deeply suppressed truth: he had been haunted his entire life by a malicious parasite of unimaginable power. Known as The Shadow King, this malevolent creature appeared in the form of Davids friend Lenny Busker (Aubrey Plaza), but was actually an ancient being named Amahl Farouk (Navid Negahban). During an epic showdown, David managed to push Farouk out of his body and gain control of his mind. With Farouk on the loose, the team formed an unlikely alliance with their former enemy, Clark DeBussy (Hamish Linklater), and his well-funded government organization, Division 3. Unfortunately, the hunt for Farouk reawakened the dark voices in Davids head, and with them, a lust for power. At odds with everyone he once considered a friend, David enlists the help of a young mutant named Switch (Lauren Tsai) whose secret ability is key to his plans to repair the damaged he caused.