A Darker Domain by Val McDermid

1984, Fife. Heiress Catriona Maclennan Grant & her baby son are kidnapped. The ransom payoff goes horribly wrong. She is killed while her son disappears without trace. 2008, Tuscany. A jogger stumbles upon dramatic new evidence that re-opens the cold case. For Detective Sergeant Karen Pirie, it's an opportunity to make her mark.