Brat Farrar - Josephine Tey

A stranger enters the inner sanctum of the Ashby family posing as Patrick Ashby, the heir to the family's sizeable fortune. The stranger, Brat Farrar, has been carefully coached on Patrick's mannerisms, appearance and every significant detail of Patrick's early life, up to his thirteenth year when he disappeared and was thought to have drowned himself. It seems as if Brat is going to pull off this most incredible deception until old secrets emerge that threaten to jeopardise the imposter's plan and his very life...