In a world where a deadly zombie virus has infected mankind, a single cure has been found. The cure, a treatment called the "Return Protein" which stays the effects of the virus in its host. With daily injections, the "Returned" are able to live as though they were never bit, despite the virus still coursing through their veins. When it is discovered that the protein stock is running low, chaos hits the streets. Returned who run out of the protein turn to zombies and wreak havoc, protestors turn to murderers as they try to rid the streets of the returned, and right in the middle of it all are Alex and Kate. Kate a leading doctor in the field of zombie virus' and Alex a musician with a dark secret, he is a Returned. As death and fear run rampant, Alex's secret becomes known and his dosage runs low, he and Kate must fight for a chance to live before he becomes a zombie.

Fifteen year-old Emma Evans has an argument with her mother Lucy since she wants to go to a concert in London with her friends Rose and Alex. Emma immediately has a convulsion and her family takes her to the hospital, but the doctors do not find any physical problem. Then her father John tries to convince his wife to send Emma to school, instead of homeschooling, but she prefers to keep Emma in the family-based education. Lucy sends her daughter to the psychoanalyst believing that she has psychological problems and Emma asks her friend Rose to record her session of hypnosis though the cellular but the doctor dies during the session. When Emma listens to the tape, she believes she is possessed by the devil and asks her parents to be submitted to an exorcism with her uncle, Priest Christopher Taylor. However her skeptical mother is against the ritual and recalls that Chris was responsible for the death of a teenager...