Science Friday - How Agatha Christie Used Chemistry To Kill (In Books)

Episode Date: August 18, 2025

Did you know that murder mystery writer Agatha Christie had a background in chemistry? In about half of her stories, the murder is committed using poison—something she was very, very familiar with. She had even trained in apothecaries to mix prescriptions by hand before she became a novelist. Chemist-turned-author Kathryn Harkup wrote about them in her new book, V is for Venom: Agatha Christie’s Chemicals of Death. Harkup talks with Host Flora Lichtman about the science of poisons, why they’re so popular in whodunnits, and how to get away with murder (in fiction writing, of course).Guest: Kathryn Harkup is a former chemist and author of V is for Venom: Agatha Christie’s Chemicals of Death.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, it's Flora Licksman, and you are listening to Science Friday. Today in the podcast, Death by Poison, with the Mistress of Mystery, the Duchess of Death, the Queen of Crime, Agatha Christie, who happened to be a chemistry nerd. You really have to be quite picky to find fault in her use of poisons. She is absolutely top quality in her scientific accuracy. In about half of Agatha Christie's stories, poison is the murder weapon of choice. Dr. Catherine Harkup, chemist-turned-author, explored those poisons in a new book, V's for Venom, Agatha Christie's Chemicals of Death. Catherine, welcome back to Science Friday.

Thank you for having me. Catherine, this is not your first book about poisons or even about Agatha Christie's poisons. What has brought you back to this well? Agatha Christie is so varied in her choice of poisons. Everyone seems to think it's just arsenic in the ubiquitous cups of tea served at the vicar's table. It's not that. She is so imaginative and creative, not just in the choice of poisons, but how they're deployed, how they're detected, how signs are signalled to her readers and other characters within the book. So I had more than enough material to fill one book. And you must love writing about the science of killing people.

Oh, who wouldn't? Okay. Well, how accurate is the poison science in Agatha Christie's books? I have to say she is top-notch. You really have to be quite picky to find fault in her use of poisons. There are certain examples where she speeds up the effects or she exaggerates the detectability, perhaps. But you can understand that for the purposes of a story. Nobody wants to read about eight hours of agonizing stomach cramps. We want to get on with the plot. So I can understand some of the shortcuts. But generally speaking, she is absolutely top quality in her scientific accuracy.

Where did she learn about poisons? She trained during the First World War to be a dispenser in a hospital dispensary. So she was making up drugs and prescriptions by hand because there was nothing pre-packaged, pre-weighed in the 1910s when the war was going on. So she just was surrounded by bottles of poisons that you had to accurately weigh out, mixed together, effectively press into pills that would hold their shape. long enough in the bottle, but disintegrate in the body to release their active component. So there is a technical skill in knowing what drugs can and can't be combined, but there is also an art in being able to blend and mix these compounds into usable products. So, and because the risk of giving someone too much or the wrong drug is very high, it has very serious consequences,

obviously you have to study very hard. You have to know. know what you're doing. So she had a very thorough background, not just in chemistry, but in pharmacy, as well as shadowing another pharmacist to understand the practicalities of this particular job. I mean, there were so many medical and science advances during Agatha Christie's time. Is there any evidence that she was keeping up with this? Oh, absolutely. I would say perhaps one of the best examples is her use of bacterial poisons. Bacteria. Bacteria. are superb poisoners. They've had millions of years to evolve very deadly, very specific toxins that enable them to live, grow, multiply. And she understood that there was a real threat if someone

got an infection and there was a very good chance that they would die. Our ability to fend off bacteria is only really a century old, less really. And Christy wrote about use. of bacteria poisons as a deliberate murder weapon pre-second World War. She didn't use it after the Second World War, probably because she realized that antibiotics gave her victims a very good chance of surviving, which is great for the victim. It's not so good when you're trying to plot a murder mystery. Wow. Do you think that the scientific accuracy made the book stronger? I think so. She has no obligation to be scientifically accurate. This is an invented world. She can be as creative, as fictitious as she wants to be. I think most readers will forgive almost anything within a story

as long as it follows its own internal logic. But to someone who appreciates how accurate it is, I think it makes it that extra special good. One of her favorite or her most cherished compliments that she received was a review by a pharmaceutical journal that complimented her on the accurate uses of poisons. Of all the reviews. Of all the reviews, just to say not whether the story was good or bad, but the use of poisons was accurate. In your book, we learn a lot about different poisons.

And I was curious about your target audience. Like, are you going for Agatha Christie diehards? chemistry nerds, serial killers. In a very selfish way, I'm going for absolutely anybody that wants to buy my book. So I am very happy to cater to Agatha Christie fans, science fans, but this is not a how-to guide. You are not going to get very far using my book as a method of planning your future murder. So there are key bits of information that are missing. I'm sorry to say, even if you are successful in your murder, you are going to be caught.

And it's very difficult to explain why you have this well-thumbed edition of my book on your bookshelves with passages underlined. Okay. So why do you think poison captures the imagination? Like, what makes it good for one of these stories? It is an incredibly devious method of murder. The idea of poisoning, you have to think about this. You really have to plan it. can't just lash out with poison. You have to figure out how you're going to obtain it, how you're going to administer it. Also, what you're going to do whilst you're waiting around for it to

take effect. So there's a lot of opportunities to think about what you're doing and reconsider. Murderers that use poison, they've got this kind of extra layer of nastiness to their personality just because they've really thought about this and continued with it. What's your favourite poison? Oh, it changes all the time. Honestly, a poison for every, every season. A poison for every season, every occasion, every mood. I get asked quite a bit, what poison would you use to kill someone?

I'm obviously not going to divulge that publicly. So I have to step around it. And I have to explain to people that obviously I would tailor my poison to my victim because what you absolutely have to do is avoid the autopsy. The people who do autopsies, forensic toxicologists, they are superb at their job and they are tenacious in finding those killer substances, which means you've got to make your murder look like natural causes or an accident. So you're going to have to have a complete medical history. You're looking for preexisting conditions and you've got to tailor your poisons to produce those symptoms. You know, I think people are familiar with nightshade and hemlock and arsenic, but Are there sort of lesser known poisons that you feel like don't get the limelight, but really should?

Don't get the publicity that they really deserve. What I try to get across to lots of people that I talk to about poisons is that poison is just the dose. Literally anything can be a poison if you give someone too much of something. So you can kill someone by giving them too much water. It takes a lot of water. they will notice and try and resist. So most poisons, most things that people think of as poisons are toxic in very small quantities. Having said that, there are all sorts of compounds that are surprisingly toxic if you take a relatively small amount.

So one of the ones that, one of the ones I particularly enjoyed researching for this book was nitroglycerin. Because we all know it as an explosive. This is what Alfred Nobel tamed and put into dynamite. This is how Alfred Nobel made his fortune and was able to bequeath these awards for the betterment of humanity through scientific and endeavors, literature and peace. But this nitroglycerin is also a very good medicine because it doesn't just disintegrate very rapidly to cause an explosion. it will disintegrate in the body to release very slowly nitrous oxide, which dilates your veins and your arteries. So if you have a constriction in the arteries feeding into your heart, then it can open them up. So it is a brilliant drug, but obviously if you take too much of it, you can dilate those vessels so much that you get a catastrophic fall in blood pressure.

Nowadays, you could not get away with murder using the poisons that Christie did. The science of why coming up after the break. The poisons that Agatha Christie used, they date her novels as much as the clothes, the conversation, the cars, etc., etc. Agatha Christie kills off a few people with Digitalis. Yes. And I recognize it from the movie Casino Royale, where Daniel Craig, as James Bond is playing poker, when he realizes his martini was laced. Who is it?

It's 007. Bon's being poisoned. He's going into cardiac arrest. Stay calm. And don't interrupt, because you'll be dead within two minutes unless you do exactly what I tell you. That's all is. What is it?

What is Digitalis? So Digitalis is, the technical name is a cardiac glycoside. So the cardiac bit is the clue. It affects the heart. There are several compounds within Foxglox. loves that produce an effect on the heart and several of them have been isolated, purified and formulated as heart drugs. They slow down heartbeat. So you get slower, more intense contractions of your heart. So if you have a rapid, fluttering heartbeat that is not efficiently pumping blood around your

body, digitalis can slow that down, coordinate it so the blood moves around your body, delivering oxygen in the way that it needs to. Obviously, if you have too much, you can slow down the heart to the point that it stops or you push it the other way and you disrupt that coordination. So Bonn's team says he has two minutes to intervene or he'll die.

Does Digitalis act that fast? Yeah, I mean, he does very quickly stagger to the bathroom to vomit and try and get rid of as much poison as possible, but obviously he doesn't get rid of it all. And he then staggers out to the car park where he's got a complete medical suite just in the glove box of his car.

So it would normally take a little longer to maybe take effect on the body, but this is a fast-paced film. So of course they speed things up. But ultimately, it's a very quick trip to the morgue if your heart stops beating. You know, I have foxglove in my garden. Yeah, so do I.

Is it the very same? Yes. So could, if I ground up the petals or something, Like what? Oh, don't make tea out of foxglove leaves. No, that's a terrible idea. Don't do that. Okay. Okay. Are there many antidotes for poison? There are quite a few antidotes. There are quite a few poisons that do have very specific antidotes. For example, opiates, morphine, heroin, drugs like that, they interact with quite specific receptors. So the antidotes are chemicals that lock into those. same receptors that don't activate them. So they literally just push the drug out of the way. So the counteracting of the effects of the drug is almost instant. It is life-saving for people who have overdosed. So that's a really specific example of an antidote. An awful lots of poisons,

however, when you turn up in an emergency ward, they will treat symptoms. So if your heart is racing, they will give you a drug that calms your heart if your heart is slow. They will give you a drug that increases the heart rate. They will treat symptoms as they present themselves until the body is stabilized. It's about keeping the patient alive and comfortable until the body can naturally break down that poison and get rid of it. You're listening to Science Friday from WNYC Studios. We're talking about the science of poison. Happy summer to you with Catherine Harcup.

Can you build a tolerance for poison? Oh, depends on the poison. So if you're thinking about something like the Dorothy Al Sayers story, strong poison, where two people eat an arsenic-laced dinner and one person survives and the other person doesn't because, spoiler, they've kind of prepared themselves by eating little doses of arsenic, that won't work. I'm afraid you're both goners.

But the science at the time was absolutely spot on. It's just that the science has discovered more. We have moved on. Okay, so Agatha Christie died in the 70s. Do you think that murderers could use those same poisons now and get away with it? Generally speaking, no. The poisons that Agatha Christie used, they date her novels as much as the clothes, the conversation, the cars, etc., etc.

Because a lot of the poisons, what we call poisons now, were part of medicine. and this is how she knew about them. But medicine has developed safer alternatives to a lot of these drugs. So you simply can't get hold of the kind of compounds Agatha Christie was dealing with. Secondly, medical care has improved dramatically, so you are more likely to survive if you have been poisoned with some of these substances. And thirdly, forensic detection is also much, much better. So you are far less likely to get away with it.

I want to get into your head a little bit. Are you having written these books just constantly scanning the room for suspicious plants? Like, has this infected your outlook? I would like to say no. There was an occasion where I went to a coffee shop with a friend, and it was a lovely coffee shop that had fresh flowers on top of their little cake display. and I looked at the fresh flowers one day and they had a particularly toxic plant

that had been picked and put into a vase and I very stupidly asked the person behind the counter if they were real or if they were fake and this particular toxic plant you can absorb the poison through your skin and to my shame she rubbed the leaves with her fingers to confirm that it was a real plant so I didn't have... That's on you

I thought twice about where certain flowers end up. What's your next book? Are you staying on the murder train? I'm afraid I am stuck on the murder train. The next book I am currently researching and I'm going through the very worst of humanity at the moment. I am writing a book on how to get away with murder or how not to get away with murder. Delightful. Catherine, thanks for joining me today.

Thank you. Dr. Catherine Harkup is the author of V is for Venom. These Chemicals of Death. Thanks for listening. Don't forget to rate and review us. Wherever you listen, it really does help us get the word out and get the show in front of new listeners. Today's episode was produced by Rasha Aredi. I'm Flora Lichtman.

Thanks for listening.