The Sinful Stones — Peter Dickinson

Scotland Yard detective James Pibble travels to a remote Scottish island to free an old man from a dangerous cult of self-proclaimed saints and saviors in this mystery by CWA Gold Dagger winner Peter Dickinson

Ninety-two-year-old Sir Francis Francis summons James Pibble to an isolated island in the Hebrides to find out who pilfered the memoirs he was in the process of writing. The Nobel Prizeâ€"winning scientist was one of the builders of the first atom bomb. Is Francis senile? Paranoid? Was the manuscript really stolen? What's the real reason he sent for Pibble?

As Pibble tries to untangle the mystery of the missing document, he starts to suspect that the devout millenarian religious sect inhabiting the island may be less virtuous than it seems; the community is strangely hell-bent on preventing Francis from ever leaving. It's up to Pibble to seek out the truth and find his own salvation before the walls of Jericho come tumbling down forever.

The Sinful Stones is the 3rd book in the James Pibble Mysteries, but you may enjoy reading the series in any order.