When the bones of a young man are found beneath the footings of a demolished house, an investigation begins that will unravel the lives of four people who have been waiting for this moment for nearly forty years, as they discover that the past can’t, and won’t, stay buried forever.

When the remnants of a body are found hidden in a river, DCI Cassie Stuart and DS Sunny Khan are faced with an impossible investigation. David Walker disappeared in 1990 at the age of 34. Only scraps of potential leads remain, but relentless work leads Cassie and Sunny to four people. Each has a connection to Walker, and a painful secret that might have driven them to murder. They are the pieces of the jigsaw Cassie and Sunny must solve. But the harder they try to put this picture together, the more blurred it becomes. It’s a case that will test their relationship in unexpected ways.

The fourth season opens with the discovery of a dismembered body in a scrap metal yard, which the team believe has been stored in a domestic freezer for thirty years. A unique Millwall Football Club tattoo leads to the victim being identified as Matthew Walsh, a young man in his mid-twenties who went missing in March 1990.