This is the story of how an infamous murder case led to the birth of modern toxicology. In the 19th century criminal poisoning with arsenic was frighteningly easy. For a few pence and with few questions asked, it was possible to buy enough poison to kill off an entire family, hence arsenic's popular name: the Inheritor's Powder. Yet if poisoning was easy, it was a notoriously difficult crime to prove. The popular press led to the nation becoming transfixed by the idea that danger lurked in every cup and on every plate. 'The fell spirit of the Borgias' was 'stalking through English society' wrote one commentator. Thus, armed with a coffee pot and some 'rat poison' one potential heir saw his opportunity. The case became a cause célèbre and led an unknown chemist, James Marsh, to develop a failsafe test.

This proved a turning point in the way such crimes were investigated - but years later there was a twist in the tale!.