Set in the fictional town of Oldcastle,[1] it follows the Misfit Mob - a detective unit of Scottish police made up of officers who were sidelined from mainstream cases for various reasons.

Tasked with what is seemingly a case of theft of a mummy from a museum, they later find that the found body was the work of a serial killer who mummifies his victims.

The Misfit Mob is where Police Scotland deposit their outcasts, troublemakers and those whom it wishes to get rid of but cannot.

Callum is in the Misfit Mob[2] because he had tampered with forensics at a crime scene, allowing a known killer to avoid conviction.

As a member of the Misfit Mob, MacGregor contends with police finding his mum's remains (25 years after she went missing) and finding out that his long lost twin brother is a serial killer who is mummifying his victims.