Agatha Christie’s murders are enmeshed with real chemistry

Celebrated mystery writer Agatha Christie authored more than 80 detective books. In many, the plot features characters killed by poisoning — with ingredients as diverse as digitalis (foxglove), strychnine and thallium. 

“[Agatha] Christie, killed over 300 people,” says Kathryn Harkup, a chemist and author of the new book "A is for Arsenic: The Poisons of Agatha Christie." "And at least 100 of those were killed by poisons.”

Harkup says Christie employed not just imaginary made up untraceable poisons. "I think her toxic tally is over 30 different compounds, which is incredible, and they are all brilliantly integrated into the plot so there's lots of chemistry and biological clues in there if you if you're looking for them.”

According to Harkup, Christie’s knowledge of chemistry is rooted in her volunteer work as a nurse during World War I.  

“This is a time when all drugs, pills, tonics, cream, etc. were made up by hand," she says. "So she [Christie] had to do a lot of studying in chemistry both theoretical and practical to make sure that she got the right dose and she didn't mix the wrong drugs to hand out to people. It was also a time when lots of compounds that you just cannot get hold of today were still being prescribed as medicines. It was a good time to be a poisoner and it was not such a good time to be on the receiving end of some of these drugs.”

In one of Christie’s fictional plots, a vicar attends a dinner party on a grand English estate. As the cocktail tray is passed around, the vicar decides to indulge in a nip. This being a mystery novel, the vicar is soon dead.

The culprit? Those who read on learn the poison used in the vicar’s drink was one most people don’t think of as a deadly element: nicotine. 

“If you have too much of anything, it will kill you, and too much of nicotine is about a gram, possibly less, which is a very small amount,” says Harkup, adding, “Mercifully for the Vicar, it's a very fast acting poison.”

Nicotine, as Harkup points out, has a terribly unpleasant taste. For a vicar equipped with British social sensibilities, however, a nasty taste in one’s drink is no reason to refuse what’s offered by a host.

“Of course he's English, he's a vicar, he can't possibly show his disgust,” Harkup says, “From a poisonous point of view, the British social crippling attitude of not making a fuss is an absolute boon. Because we will just swallow down anything not to look embarrassed or show ourselves up. So he determinedly swallows down this drink which he doesn't like, and it's the end of him.”

Christie’s chemically-astute descriptions of poisons are so scientific, that there are actually recorded cases of people using her fictional setups to attempt murder themselves, or to rescue lives.

“Her descriptions of poisoning are so accurate … particularly the more unusual poisons,” Harkup says, “There was a case in South America, and in the UK, that people, because they’d been reading Agatha Christie's novel ‘The Pale Horse,’ they recognized the symptoms of thallium poisoning. And they were able to get doctors to intervene and administer the antidotes and save these people's lives.”

This article is based on an interview that aired on PRI's Science Friday with Ira Flatow.

A previous version of this story incorrectly stated the poison of choise in The Pale Horse.