Aaron Elkins - Old Bones

With the roar of thunder and the speed of a galloping horse comes the tide to Mont St. Michel goes the old nursery song. So when the aged patriarch of the du Rocher family falls victim to the perilous tide, even the old man's family accepts the verdict of accidental drowning.
But too quickly, this "accident" is followed by a bizarre discovery in the ancient du Rocher chateau: a human skeleton, wrapped in butcher paper, beneath the old stone flooring.
Professor Gideon Oliver, lecturing on forensic anthropology at nearby St. Malo, is asked to examine the bones. He quickly demonstrates why he is known as the "Skeleton Detective," providing the police with forensic details that lead them to conclude that these are the remains of a Nazi officer believed to have been murdered in the area during the Occupation.
Or are they? Gideon himself has his doubts. Then, when another of the current du Rochers dies—this time via cyanide poisoning—his doubts solidify into a single certainty: someone want old secrets to stay buried … and is perfectly willing to eradicate the meddlesome American to make that happen.