Amid societal unrest in 1984, oil heiress Catriona Grant and her son Adam are kidnapped at gunpoint, but after sending two ransom notes the culprits unexpectedly fall silent and the pair are never seen again. When a man's body is discovered 40 years later in a quarry with a piece of evidence connected to the case, DI Karen Pirie is tasked with reopening the case with the first new lead in decades.