To Make an Underworld — Joan Fleming

When Robert Escrick, the former chairman of the family firm, decides to disappear because the company is being taken over, he retires early, changes his name and sets off for Cornwall, accompanied by his dog Banjo. His wife won't notice he's gone, and he's had a house built for him in preparation. But there is a young woman waiting for him there, locked in a bathroom and claiming to have been raped, and the locals take her part against the newcomer. Then she is found murdered, and reality starts closing in on the retreat Robert has escaped to ...