Susannah Cahalan an up-and-coming journalist at the New York Post, and she’s falling in love with a musician named Stephen. When her boss gives her the big assignment that will jumpstart her career, things couldn’t be better.
Soon little things start going wrong. Susannah gets a flu she can’t shake, she forgets things, and she misses deadlines at work. She can hear people talking about her, she’s sure that Stephen has another girlfriend, and she can’t control her body. It soon gets worse; Susannah begins having violent seizures, and her increasingly psychotic behaviour means she must be watched at all times.
After repeated trips to the hospital, a team of doctors can find nothing wrong with her. As Susannah is admitted and spends days, then weeks, in a hospital bed losing her ability to move, talk, even eat, her family is repeatedly told that she is one hundred percent healthy. Her mom and dad are at a breaking point, waiting for their daughter to die while being told there is nothing anyone can do to help her.
Only when they finally find a doctor determined and curious enough to see her case through can Susannah begin to recover from her bizarre illness and try to get back to the vibrant young woman she was.