When a man is found murdered in gruesome circumstances, Merrily becomes convinced Satanists are operating in the city. The next morning, she is called to Hereford General Hospital to perform an exorcism. The nurses are treating an ill man known for his cruelty towards animals and his abuse of women. They believe the ward has become polluted by his dark nature. Merrily begins to feel the force of his depravity as the life force in his body begins to ebb away. After feeling shaken and violated by her experience, Merrily begins to wonder if the two deaths could be connected. Merrily begins to give expertise on the case to the police team - DCI Annie Howe and DS Frank Bliss - who are investigating the case. Not all seems right when their enquiries take into a dark and dangerous world.

Merrily Watkins, a single mother who is not your average country vicar. Her newly acquired training in the works of exorcisms has pulled her to the dark side of the pulpit. She has become one of the very few women priests who are working as exorcists - a job which is mistrusted by the modern church and rarely ever talked about. Merrily is joined by Rev Huw Owen, a deliverance ministry tutor and Merrily's mentor. Her advanced and excessive knowledge of the paranormal underworld brings her to the notice of the local police who need her help. The force need her advice on the investigation of a grisly murder. However Merrily is still going through the motions of losing her late unfaithful husband, Sean, in a car crash. She seeks shelter in her job despite having a 16-year-old daughter, Jane. After the discovery of a gruesome murder, Merrily becomes convinced that Satanists are operating in the city.