In 19th Century New York City, capital punishment has been replaced by The Machine, a strange device that forces sentenced criminals to suffer the pain and fear of their own victims' murder. Though it does not execute them, most wish they were dead. Apothecary Justin Briggs is the sole detective sanctioned to use the device to see the final moments of a victim's life and thereby identify the killer, a process called Talion. When a young official is sent by Washington to inquire into the constitutionality of the new system, a series of strange killings perpetrated by a masked man grips the city. As the death toll rises, Mr. Briggs must find a way to defeat the murderer - and his own demons.