When a young Jewish man dies suddenly during prayers, Dr. Ogden suspects arsenic poisoning and concludes that others may be falling victim to a poisoner.

While investigating a murder, Murdoch finds himself teamed with a North-West Mounted Policeman from British Columbia whose methods and mannerisms are strikingly similar to this own -- perhaps too similar? The Mountie believes the Toronto homicide is related to a case he is investigating. Murdoch hopes to rekindle his relationship with Dr. Ogden -- but is it too late?