With two bodies in the morgue, Richter and Diana make a discovery which connects Sinead and Ronan to a historical case called the Mountain Murderer.

A murderer revealed, the race is on to find Sinead but when hope is lost, the case is closed until an unexpected return marks a new beginning.

The extent of danger the town faces unfolds. Aileen risks everything and when Diana and Richter finally face the murderer he has to conquer his demons if he wants to survive.