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A is for Arsenic: The Poisons of Agatha Christie

November 13, 2015


We spoke to chemist, writer and Agatha Christie fan, Kathyrn Harkup, about her fascinating new book, A is for Arsenic, which takes a look at fourteen Agatha Christie novels and investigates the poisons used. 

Agatha Christie used poison to kill her characters more often than any other murder method, with the poison itself a central part of the plot. With gunshots or stabbings the cause of death is obvious, but not so with poisons. How is it that some compounds prove so deadly, and in such tiny amounts?

What many readers may not realise is that her choice of deadly substances was far from random. The chemical and physiological characteristics of each poison had been thoroughly researched by Christie and provide vital clues to discovery of the murderer.

A is for Arsenic looks at why certain chemicals kill, how they interact with the body, and the feasibility of obtaining, administering and detecting these poisons, both at the time the novels were written and today. Kathryn Harkup spoke to us about the inspiration behind the book, her favourite Christie novels and how her heroine knew so much about this topic…


What inspired you to write a book about the poisons used in Agatha Christie’s novels?

I became interested in poisons when I read a review of a book, Periodic Tales. The review said that, at one point in history, arsenic had been so commonly used in murder that it became known as ‘inheritance powder’. At the time I was working for a university running programmes to engage young people in science and engineering and I knew that anything disgusting or dangerous was the best way to engage bored teenagers. Poisons were the perfect topic. I had worked with quite a few toxic compounds when I was working in a chemistry lab, so knew the basics of their toxicity and how to work with these compounds safely, but I had to do a lot more research. Many of the books I read on toxicology and poisons mentioned Agatha Christie and her frequent and accurate use of poisons. So, when I was asked by Bloomsbury if I wanted to write a book, poisons and Agatha Christie seemed an obvious choice.


Obviously you’re a big fan of Christie. Which are your favourite novels? Do you prefer the ones where poison is the killing method?

I have many favourites and they change regularly but I don’t always pick novels that feature poison. At the moment my favourites are …

1) And Then There Were None – for a great idea brilliantly delivered. Ten people are stranded on an island and one by one they are all killed. It seems to be an impossible puzzle but of course Christie has the solution.

2) Five Little Pigs – for an excellent example of how the symptoms of poisoning give vital clues that lead Poirot to the murderer. Christie used a classic poison in this novel, hemlock, and goes in to some detail about its history.

3) The Murder of Roger Ackroyd – for the twist at the end. When it was first published it caused outrage because readers complained Christie had ‘cheated’. Now it is considered a classic of crime fiction.

4) The Pale Horse – for the scientific accuracy. Thanks to Christie’s detailed descriptions of the poison’s symptoms, this novel has been credited with saving two people from thallium poisoning.

5) Why Didn’t They Ask Evans? – for the sheer fun of it.


How much did your own background as a chemist help in the writing of this book?

My chemistry background helped a lot in terms of not being daunted by delving into the scientific literature but Christie knew far more about poisons and their effects than I did. I had a lot of catching up to do and a lot of biology to learn. Although some readers of A is for Arsenic might not be expecting the scientific detail I included, I felt it was important to explain how these poisons work to show just how good Christie was. She must have done a huge amount of research to maintain such a high standard. The science of these poisons have a fascinating history in their own right, something that Christie alluded to in her novel Curtain, and I wanted to share some of these fantastic stories.


Christie’s knowledge of poisons was more precise than people might realise. How did she gain such a thorough real-world knowledge of poisons?

Christie trained as a dispenser in a hospital during the First World War. At this time the majority of prescriptions were made by hand. Dispensers had to understand theoretical and practical chemistry to combine the right compounds, in the correct dosage, to formulate pills, creams and tonics. There were a lot of checks in place but Christie had first-hand knowledge of how easily mistakes could be made and the consequences of giving to someone too large a dose could be very serious.

Her detailed understanding not just of individual drugs but of how they could work in combination gave her huge flexibility in her plots. She could manipulate time-lines by delaying the effects of poisons or make innocuous substances lethal by swapping medications, for example eye-drops for insulin. Such depth and breadth of knowledge allowed her to be highly inventive in her methods of murder.


How accurate was Christie in her descriptions of murders by poisoning ? Did she make any gaffes or were the doses and the effects mostly accurately described?

Christie was amazingly accurate with very few errors. The few mistakes she did make are relatively minor, however, one short story, The House of Lurking Death, is probably the most inaccurate. In this story Christie used ricin to kill her victims but the method of delivery is not very plausible. The time taken for the victims to die and the speed that ricin was identified is far too quick. Christie wrote this story nearly 50 years before the first known ricin murder was committed (Georgi Markov on Waterloo Bridge in London) so it’s not surprising she got a few things wrong. But, she did get an awful lot right for example, how her murderer could have obtained ricin and how they could eat the same poisoned sandwiches as the victims, yet survive.


With the advances of science today, are poisons now much easier to detect than they were in Christie’s day, making poisoning an old-fashioned kind of killing method or is poisoning still used as a murder method today?

There are thankfully far fewer poisoning cases today than there were in the nineteenth century and even in Christie’s day. Poisonings do still occur but they are no longer in the domestic settings that Christie wrote about. The sale of poisonous compounds is much better regulated meaning it is difficult for the average person on the street to get hold of these substances. Recent cases tend to be carried out by those that have more access to poisons, such as the doctor Harold Shipman, and political poisonings such as dioxin given to the Ukranian President Viktor Yushenko.


Who would you expect this book to appeal to – Agatha Christie fans interested in poisons as well as chemists who are Agatha Christie fans? Crime fiction fans in general?

I hope there is something in the book for everyone, whether you are interested in true-crime, Agatha Christie or the science of poisons and medicine. I’m fascinated by all these aspects and especially how all of these apparently diverse topics overlap. Scientific research into poisons has led to medical discoveries; murder cases have led to advances in detection, and crime fiction has led to the detection of poisoning cases. Agatha Christie effortlessly combines all these aspects of poisoning in her stories. She name-drops real-life poisoners, uses real murder cases as plot lines, and draws on her scientific knowledge to create clues, false-leads and red-herrings.


It’s 125 years since Agatha Christie’s birth. Do you think she is enjoying a resurgence in popularity?

I hope so. Christie’s novels have often been derided for poor characterisation and their simple writing style. To me her characterisation is economical rather than poor, giving her space to crack on with the plot, and her easy writing style hides detailed and complex plotting. There is a cosy nostalgia to sitting down with an Agatha Christie. We know that the bad guys will, almost always, be punished and the good guys will, almost always, live happily ever after, but there is much more to it than that. I think many people read Christie for the same reason we do crossword puzzles and brain teasers. Christie set top quality puzzles that we try and solve before the detective. Even though we know to look for plot twists and examine all the clues carefully, it is still a surprise when the murderer is finally identified.


You’re a scientist who has turned to writing and managed to combine both skills with fascinating books such as ‘A is for Arsenic’. Are there plans for any similar books in the future?

harkup, kathryn

The next book is also looking at the scientific background to a novel but this time it is Mary Shelley’s Frankenstein. It is an exceptional debut novel that spawned an entire genre of fiction, science fiction, written at the age of only nineteen. There are going to be lots of stories of body snatchers, alchemists and electrocuting frogs. I’m really looking forward to it.


A is for Arsenic by Kathryn Harkup, published by Bloomsbury Publishing. To find out more or purchase a copy click here



  1. Deborah Finnerty

    What a fantastic book it will be. I cannot wait to get a copy. I’m sure Kathyrn Harkup will find she has many fans. Agatha Christie was an amazing author and is loved by many as I am sure Kathyrn will be.

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