Dr. Arthur Calgary takes a ferry across the Rubicon River to Sunny Point, the home of the Argyle family. A year before, the matriarch of the family was murdered and Jack, the son, was convicted and sentenced to life in prison. Throughout the trial Jack had maintained his innocence, claiming he had hitchhiked on the night of the murder and had been picked up by a middle-aged man. Calgary was the stranger in question. 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...