If you looks at any newspaper from the early 1900s, its advertising content is surprisingly similar to today's. There have always been cure-all elixirs to fix all of your ailments. Just like today, it sometimes takes awhile for the authorities to figure out that some of these mysterious new chemicals and compounds are, in fact, very very bad for you. But back in the day, it was a heck of a lot easier to accidentally die of poisoning, or even poison someone on purpose, because there was very little regulation or ways to prove what happened. In the early 1920s, almost a thousand New Yorkers died every year because of poisoning.
Enter New York City medical examiner Charles Norris in 1918. Shockingly, he was the first medically trained medical examiner to be appointed in the city (it was not a requirement... they could be a garbageman, carpenter, accountant, or best friend of the mayor). When he was hired in 1918 things started changing, as he insisted that mysterious poisioning deaths be investigated by his team, including his chief toxicologist Alexander Gettler. Gettler's conclusions based on scientific tests on body tissue took a little time to catch on, but when he was able to prove in court the guilt or innocence of people accused in poisoning deaths, people started to take notice.
The Poisoner's Handbook is filled with re-enactments of famous New York City poisoning cases from the era, as well as scenes of Gettler and his team methodically doing the tests in their labs. Cases included young women watch painters dying of horrific radiation poisoning (they licked the paintbrushes while painting glowing radium dots on the watch faces), as well as a couple that inadvertantly died of poison gas (for pests) coming from the basement of their building through the vents, and a woman that was tried (and freed) for poisoning her brother, and later tried (and convicted) for poisoning another man.
This is really really fascinating stuff. It is hard to imagine crime investigation before true, tested scientific proof came into the picture. After watching this show, Alexander Gettler is my new science hero!