John Parsons Cook was a 28 year old bachelor, from a good family but not in robust health. He studied to become a lawyer, but instead of following that career, turned to raising race horses. In November 1855, during a visit to the Shrewsbury races, he was taken violently ill. He was attended by the 80 year old local doctor Dr. Bamford, and Cook's friend and sometimes partner, Dr. Palmer.

William Palmer was a physician and surgeon, a widower and father. His appearance instilled confidence and invited trust. But were appearances deceptive? Was he, in fact, a cool, calculating and vicious serial murderer, who used his knowledge and skill for evil ends, to escape the effects of an addiction that was destroying his life? There are numerous references to this case in fiction, by Dickens, Sayers, Hitchcock and others; and the familiar salutation "What's your poison?" is believed to date from the events of this case. This is true courtroom drama, more gripping than fiction and it will have you guessing until the end.