The House at Sea's End: The Dr Ruth Galloway Mysteries 3 by Elly Griffiths
Dr Ruth Galloway is called in by a team of archaeologists investigating coastal erosion on the north Norfolk coast, when they unearth six bodies buried at the foot of a cliff. They seem to have been there a very long time. Ruth must help discover how long, and how on earth they got there.
Ruth and DCI Nelson are drawn together once more to unravel the past. Tests reveal that the bodies have lain, preserved in the sand, for sixty years. The mystery of their deaths stretches back to the Second World War, a time when Great Britain was threatened by invasion.
But someone wants the truth to stay buried, and will go to any lengths to keep it that way... even to committing murder.