When Detective Erika Foster receives a tip off that key evidence for a major narcotics case was stashed in a disused quarry on the outskirts of London, she orders for it to be searched. From the thick sludge the drugs are recovered, but so is the skeleton of a young child. The remains are quickly identified as seven-year-old Jessica Collins. The missing girl who made headline news when she vanished twenty-six years ago. As Erika tries to piece together new evidence with the old, she discovers a family harbouring secrets, a detective plagued by her failure to find Jessica, and the mysterious death of a man living by the quarry.