One of the best episodes yet in a very high quality series.
When a young man is found shot to death in a notorious mob area, John is stunned by the remarkable resemblance of the victim to one of his sons from the early 1800's. When he discovers that the young man was from a very old local family - now turned mobsters - he becomes more convinced than ever that he is now investigating the death of a direct descendant of his. He makes it personal family business to find the killer and bring him to justice.
This episode deals with some of the unhappiness John has had to live with, as those he loves become old around him and at some point, he has to leave them and move on, breaking their very mortal hearts in the process.
A touching, poignant episode, it allows us yet more insight into the pain of being apparently immortal and the effect that has on the lives of those around you.