Susannah Cahalan, an up-and-coming journalist at the New York Post becomes plagued by voices in her head and seizures, causing a rapid descent into insanity.

Chloë Grace Moretz
as Susannah Cahalan

Thomas Mann
as Stephen Grywalski

Richard Armitage
as Tom Cahalan

Carrie-Anne Moss
as Rhona Nack

Jenny Slate
as Margo

Tyler Perry
as Richard

Alex Zahara
as Allen

Jenn MacLean-Angus
as Giselle

Ken Tremblett
as Senator

Navid Negahban
as Dr. Najjar