How Agatha Christie Used Chemistry To Kill (In Books)

FLORA LICHTMAN: This is Science Friday. I’m Flora Lichtman. Perhaps no other author has been more influential in the crime-writing genre than the Mistress of Mystery, the Duchess of Death, the Queen of Crime, Agatha Christie.

She has sold billions of books. They’ve been translated into over 100 languages. But did you know that Agatha Christie had a chemistry background? In about half her stories, poison is the murder weapon of choice, something Christie knew a little bit about.

Dr. Kathryn Harkup, chemist turned author, explored those poisons in a new book, V is for Venom– Agatha Christie’s Chemicals of Death. Kathryn, welcome back to Science Friday.

KATHRYN HARKUP: Thank you for having me.

FLORA LICHTMAN: Kathryn, this is not your first book about poisons or even about Agatha Christie’s poisons. What has brought you back to this well?

KATHRYN HARKUP: 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 signaled to her readers and other characters within the book. So I had more than enough material to fill one book.

FLORA LICHTMAN: And you must love writing about the science of killing people.

KATHRYN HARKUP: Oh, who wouldn’t?

FLORA LICHTMAN: OK. [LAUGHS] Well, how accurate is the poison science in Agatha Christie’s books?

KATHRYN HARKUP: 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.

FLORA LICHTMAN: Where did she learn about poisons?

KATHRYN HARKUP: 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, mix 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.

And because the risk of giving someone too much or the wrong drug is very high and it has very serious consequences, obviously, you have to study very hard. You have to 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.

FLORA LICHTMAN: 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?

KATHRYN HARKUP: Oh, absolutely. I would say perhaps one of the best examples is her use of bacterial poisons. 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 Christie wrote about the 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.

FLORA LICHTMAN: Wow. Do you think that the scientific accuracy made the book stronger?

KATHRYN HARKUP: I think so. I mean, 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.

FLORA LICHTMAN: [LAUGHS] Of all the reviews.

KATHRYN HARKUP: Of all the reviews, just to say not whether the story was good or bad, but the use of poisons was accurate.

FLORA LICHTMAN: [LAUGHS] In your book, we learn a lot about different poisons. And I was curious about your target audience. Are you going for Agatha Christie diehards, chemistry nerds, serial killers?

KATHRYN HARKUP: In a very selfish way, I’m going for absolutely anybody that wants to buy my book.

FLORA LICHTMAN: [LAUGHS]

KATHRYN HARKUP: So I–

FLORA LICHTMAN: Of course, certainly.

KATHRYN HARKUP: I’m 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.

FLORA LICHTMAN: OK, so why do you think poison captures the imagination? What makes it good for one of these stories?

KATHRYN HARKUP: It is an incredibly devious method of murder. The idea of poisoning, you have to think about this. You really have to plan it. You 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.

FLORA LICHTMAN: What’s your favorite poison?

KATHRYN HARKUP: Oh, it changes all the time. Honestly–

FLORA LICHTMAN: A poison for every season.

KATHRYN HARKUP: 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 pre-existing conditions. And you’ve got to tailor your poisons to produce those symptoms.

FLORA LICHTMAN: I think people are familiar with nightshade and hemlock and arsenic. But are there lesser-known poisons that you feel like don’t get the limelight, but really should?

[LAUGHTER]

KATHRYN HARKUP: Don’t get the publicity that they really deserve.

FLORA LICHTMAN: Yeah.

KATHRYN HARKUP: [LAUGHS] 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.

FLORA LICHTMAN: Such as?

KATHRYN HARKUP: So one of the ones that– one of the ones I particularly enjoyed researching for this book was nitroglycerin, because we all 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 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.

FLORA LICHTMAN: Agatha Christie kills off a few people with digitalis.

KATHRYN HARKUP: Yes.

FLORA LICHTMAN: 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.

[VIDEO PLAYBACK]

– Who is it?

– 007.

– Bond’s been 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.

– I’m all ears.

[END PLAYBACK]

FLORA LICHTMAN: What is it? What is digitalis?

KATHRYN HARKUP: 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 foxgloves 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.

FLORA LICHTMAN: So Bond’s team says he has two minutes to intervene or he’ll die. Does digitalis act that fast?

KATHRYN HARKUP: 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.

FLORA LICHTMAN: I have foxglove in my garden.

KATHRYN HARKUP: Yeah, so do I.

FLORA LICHTMAN: Is it the very same?

KATHRYN HARKUP: Yes.

FLORA LICHTMAN: So if I ground up the petals or something, what–

KATHRYN HARKUP: Oh, don’t make tea out of foxglove leaves. No. That’s a terrible idea. Don’t do that.

FLORA LICHTMAN: OK. [LAUGHS] OK. Are there many antidotes for poison?

KATHRYN HARKUP: 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 but 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 lifesaving for people who have overdosed. So that’s a really specific example of an antidote.

An awful lot 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.

And 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.

FLORA LICHTMAN: You’re listening to Science Friday from WNYC studios. We’re talking about the science of poison. Happy summer to you, with Kathryn Harkup. Can you build a tolerance for poison?

KATHRYN HARKUP: Ooh, depends on the poison. So if you’re thinking about something like the Dorothy L. 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.

FLORA LICHTMAN: So Agatha Christie died in the ’70s. Do you think that murderers could use those same poisons now and get away with it?

KATHRYN HARKUP: Generally speaking, no. The poisons that Agatha Christie used, they date her novels as much as the clothes, the conversation, the cars, et cetera, et cetera. 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.

FLORA LICHTMAN: I want to get into your head a little bit. Are you, having written these books, just constantly scanning the room for suspicious plants? Has this infected your outlook?

KATHRYN HARKUP: Um. [SIGHS] I would like to say no.

[LAUGHTER]

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–

FLORA LICHTMAN: That’s on you.

KATHRYN HARKUP: I thought twice about where certain flowers end up.

FLORA LICHTMAN: What’s your next book? Are you staying on the murder train?

KATHRYN HARKUP: 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.

FLORA LICHTMAN: Delightful. Kathryn, thanks for joining me today.

KATHRYN HARKUP: Thank you.

FLORA LICHTMAN: Dr. Kathryn Harkup is the author of V is for Venom– Agatha Christie’s Chemicals of Death. Before we go, we are working on a show about how social media algorithms are changing the way we write and talk. And we want to hear from you.

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[MUSIC PLAYING]

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