Karen Pirie

At St Andrews Police Station in Scotland, DS Karen Pirie is often overlooked and underestimated by her colleagues. One day, she is unexpectedly tasked with reopening a 25-year-old cold case: the 1996 murder of 19-year-old Rosie Duff at the cathedral. Although three men were found at the scene, they were never charged. When one of them, Malkiewicz, is killed in a hit-and-run while jogging, Pirie officially launches her investigation team to uncover the long-buried truth.

A young detective named Mint joins the cold case team. The remaining two witnesses are Tom Mackie and Alex Gilbey. As Mint hustles to gather evidence, DNA testing reveals that Rosie's daughter is alive. Meanwhile, Mackie, whose past behavior included stalking women, is mocked as an eccentric deviant. Under intense police pressure, he eventually falls from a cliff into the sea.

[Season Finale]Gilbey is finally arrested on suspicion of murdering Rosie. Though his past relationship makes him a prime suspect, he maintains his innocence and is released. However, he is soon shot by a girl stalking him, and his newborn baby is abducted. As the cold case team hits a dead end without decisive evidence to arrest the real killer, an unexpected and shocking truth finally comes to light, changing everything they thought they knew about the case.