The Chessmen (The Lewis Trilogy, 3) by Peter May

THE NEW START. Fin Macleod, now head of security on a privately owned Lewis estate, is charged with investigating a spate of illegal game-hunting taking place on the island. THE OLD FRIEND. This mission reunites him with Whistler Macaskill – a local poacher, Fin’s teenage intimate, and possessor of a long-buried secret. THE FINAL CHAPTER. But when this reunion takes a violent, sinister turn and Fin puts together the fractured pieces of the past, he realizes that revealing the truth could destroy the future.