DCI Matthew McCallum is a cultured copper, overseeing major crime for Police Scotland in Edinburgh and surrounding areas. A few months from retirement, he is hoping for a quieter life, but another case of murder hits his desk, closely followed by two more cases.

A man hanging in his house, a woman brutally stabbed to death and an arson attack on a community centre stretch his team to the limit. Devil symbology is left at each crime scene, leading them to conclude that they have a serial killer on their hands.

Just as the situation threatens to get out of control, they catch a break and apprehend a suspect. However, it soon becomes clear that the person they have in custody is only one small part of a dark and disturbing plan.

The killing doesn't stop, leading Matthew and his team on a wild and frightening journey to discover the real reasons behind the murder spree.

Will Matthew be able to crack The Devil's Code?