Throughout his trial Jack had maintained his innocence, claiming he was hitchhiking on the night of the murder and he had been picked up by a middle-aged man in a dark car. Unable to locate this mystery man the police viewed Jacks story as a lie. Dr Arthur Calgary was the stranger in question, but he arrives too late for Jack - who succumbs to pneumonia after serving just six months of his sentence. Feeling a sense of duty to the Argyles, Calgary is surprised when his revelation has a disturbing effect on the family - it means one of the family is a murderer.