The past won't stay buried forever.

November, 1957: Six teenage girls walk in the churning Derbyshire mists, the first chills of winter in the air. Their voices carrying across the fields, they follow the old train tracks into the dark tunnel of the Cutting. Only five appear on the other side.

October, 2014: a dying mother, feverishly fixated on a friend from her childhood, makes a plea: 'Find Valerie.' Mina's elderly mother had never discussed her childhood with her daughter before. So who was Valerie? Where does her obsession spring from?

DC Connie Childs, off balance after her last big case, is partnered up with new arrival to Bampton, Peter Dahl. Following up on what seems like a simple natural death, DC Childs' old instincts kick in, pointing her right back to one cold evening in 1957. As Connie starts to broaden her enquiries, the investigation begins to spiral increasingly close to home.