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?