Priest and trainee exorcist Merrily Watkins has barely started in her new role when she is asked by the police for her help in solving a baffling and gruesome murder. Quickly caught up in a terrifying mystery, Merrily soon finds herself in real danger.

A second murder, a desecrated church and the apparent suicide of a clergyman send Merrily on a quest for answers. Although she suspects a Satanic group may be at work, nothing can prepare Merrily for what she uncovers next.

Drained physically and emotionally by her own demons, the last thing Merrily wants to do is battle anybody else's. Spurred on by mentor Huw Owen, Merrily puts the final pieces of the jigsaw into place and soon realises that she must find the strength to fight evil if she is to save her daughter's soul.