Enhanced descriptions from Syndetics:

THE FINAL VOLUME IN PETER MAY'S LANDMARK LEWIS TRILOGY
"MAGICAL." -- KIRKUS REVIEWS
"UTTERLY ABSORBING." -- BOOKLIST (STARRED REVIEW)
"A PERFECTLY FORMED TRILOGY." -- THE INDEPENDENT

Living again of the Isle of Lewis, ex-Detective Inspector Fin Macleod is working as a security officer for a local landowner. While investigating illegal activity on the estate, Fin encounters his former childhood friend and bandmate, the elusive poacher Whistler Macaskill.
When Fin catches up with Whistler among the windswept hills of the estate, the two witness a freak natural phenomenon--a bog burst--which drains a loch of all its water in a flash, revealing a mud-encased light aircraft with a sickeningly familiar moniker on its side.
Both men immediately know what they will find inside: the body of Roddy Mackenzie, a friend whose flight disappeared more than seventeen years before. But when Whistler's face appears to register something other than shock, an icy chill of apprehension overtakes Fin. What secret has Whistler been hiding from him, and everyone else on the island?