The Lewis Man by Peter May

A MAN WITH NO NAME. An unidentified corpse is recovered from a Lewis peat bog; the only clue to its identity being a DNA sibling match to a local farmer. A MAN WITH NO MEMORY. But this islander, Tormod Macdonald – now an elderly man suffering from dementia – has always claimed to be an only child. A MAN WITH NO CHOICE. When Tormod’s family approach Fin Macleod for help, Fin feels duty-bound to solve the mystery.