Agatha Christie 
Ordeal by Innocence 

Evidence that clears the name of a boy sentenced for killing his adopted mother arrives too late to save his life – so who did kill her?According to the courts, Jacko Argyle bludgeoned his mother to death with a poker. The sentence was life imprisonment But when Dr Arthur Calgary turns up a year later with the proof that confirms Jacko’s innocence, he is too late – Jacko died behind bars from a bout of pneumonia.Worse still, the doctor’s revelations re-open old wounds in the family, increasing the likelihood that the real murderer will strike again…