Priest and trainee exorcist Merrily Watkins is asked for help by police in solving a baffling and gruesome murder. She quickly becomes embroiled in a terrifying mystery and finds herself in real danger.

Merrily is on a quest for answers after a murder, a desecrated church and a clergyman's apparent 'suicide'. She suspects a Satanic group may be at work, and is guided through a ceremony of lesser exorcism by Huw Owen, but nothing can prepare her for what she is about to uncover.

Exhausted by her own demons, battling anyone else's is the last thing Merrily wants to do. However, she must gather her wits and take strength from her mentor Huw Owen as she puts the final pieces of the jigsaw into place. As the investigation reaches its conclusion, Merrily realises she needs to steel herself and summon the energy to fight evil in order to save her daughter's soul.