When Professor Francombe and her team of archaeologists find the remains of three women on a remote Kintyre hillside - a site rumoured to have been the base of Viking warlord Somerled - their delight soon turns to horror when they realise the women tragically met their end little more than two decades ago.
It soon becomes clear that these are the three missing victims of the `Midweek Murderer', a serial killer who was at work in Glasgow in the early 1990s. DCI Jim Daley now has the chance to put things right - to confront a nightmare from his past and solve a crime he failed to as a young detective.
However, when Police Scotland's Cold Case Unit arrive, they bring yet more ghosts to Kinloch. A tale of death, betrayal, Viking treasure and revenge set in the thin places where past, present and future collide.