James Phyllis. Unnatural Causes

The third book in the Inspector Adam Dalgliesh series, 1967
Superintendent Adam Dalgliesh was looking forward to a quiet holiday at his aunt's cottage on Monksmere Head. There would be long walks, tea in front of the fire, and, best of all, no corpses. But he reckoned without the discovery of crime-writer Maurice Seton's mutilated body.
P. D. James is the author of twenty-one books, most of which have been filmed for television. She spent thirty years in various departments of the British Civil Service, including the Police and Criminal Law Departments of Great Britain’s Home Office. She has served as a magistrate and as a governor of the BBC. The recipient of many prizes and honours, she was created Baroness James of Holland Park in 1991 and was inducted into the International Crime Writing Hall of Fame in 2008. She lives in London and Oxford.