Christie, Agatha -- Ordeal by Innocence (1958)

Blurb: Young Jacko Argyle had died in a prison hospital after serving only six months of a life sentence for the murder of his mother.  There had been no room for argument or doubt about his guilt and not even his family could regret his passing.  But now, more than ten years afterwards, a stranger climbed the hill up from the ferry with news which ripped the peace of the household into shreds.  Could Jacko’s alibi have been proved after all?  If it could, then a terrifying situation existed for the handful of people who fulfilled the classic formula: Motive, Means and Opportunity.  Fear and suspicion spread among them like a disease as they were subjected to the agony of doubt and suspicion.

Ordeal by Innocence combines another dazzling demonstration of the Christie guile and skill with a convincing and brilliant study of a family who found that they were living with murder.