The BBC’s lavish adaptation of Agatha Christie’s The Pale Horse reached its gripping conclusion on Sunday.
Yet few of those enthralled by its tale of mystery and murder know of the strange afterlife of this remarkable novel.
That is because The Pale Horse, written by the Queen of Crime in 1961, is credited with having inspired at least two high-profile killings: the Teacup Poisoner and the Mensa Murder.
The book’s climax — as anyone who watched the TV version will know — turns on the almost undetectable effect of poisoning by thallium, a salt obtained from the rare heavy metal of the same name.
This has led to it being dubbed ‘the poisoner’s poison’.
The BBC’s lavish adaptation of Agatha Christie’s The Pale Horse (cast pictured) reached its gripping conclusion on Sunday but the novel is credited with having inspired at least two high-profile killings
In the words of an eminent pathologist, Christie’s novel provides ‘one of the few reliable descriptions of thallium poisoning outside a specialist text’.
Dr Kathryn Harkup, author of A Is For Arsenic: The Poisons Of Agatha Christie, says: ‘Thallium is relatively unknown and thallium poisoning is extremely hard to diagnose.
‘It can produce a range of symptoms — it affects the nerves, causes hair to fall out, flu-like symptoms, pneumonia — all of which you’d be likely to attribute to other causes. You can read Christie’s book as a sort of guide to thallium poisoning.’
Is that what the notorious serial killer Graham Young did? He killed at least two people with thallium and poisoned several more. Young may have been inspired by Christie’s book — and he was only caught because of it.
His trial attracted blanket coverage in the Press and he has gone down in history as the Teacup Poisoner because he delivered his fatal doses in his victims’ daily cuppas.
Teacup Poisoner Graham Young (pictured) killed at least two people with thallium and poisoned several more. Young may have been inspired by Christie’s book — and he was only caught because of it
Young’s fatal attraction to poisons and poisoning started early. A solitary, withdrawn child, he would spend hours in his room experimenting with a chemistry set and earned the nickname of the ‘Mad Professor’ at school.
He poisoned his first subjects at the age of nine or ten, using toxins stolen from his school laboratory. These he administered to his friends in sandwiches and soft drinks.
He also poisoned frogs and the family cat. By the time he was 13, he had stockpiled a collection of more potent chemicals by convincing local chemists that he needed them for scientific experiments.
His first victim was his hated stepmother Molly. He began lacing her tea with belladonna, the toxic extract of the deadly nightshade plant, before moving on to the metallic poison antimony and — when it seemed she’d developed a resistance to that — thallium.
Her eventual death was initially attributed to complications from an earlier car accident, but an aunt grew suspicious, a psychiatrist was called and Young eventually confessed to the killing and also poisoning his father and sister — both of whom survived — with antimony.
He was committed to Broadmoor psychiatric hospital but released in February 1971 after eight years, having been pronounced cured.
Indeed, the psychiatrist Edgar Udwin judged that Young had ‘completely recovered’ and ‘was no longer obsessed with poisons, violence and mischief’.
Almost unbelievably, he soon got a job as a storeman at John Hadland Laboratories in Bovingdon, Hertfordshire, which manufactured infrared lenses using . . . thallium.
Few of those enthralled by its tale of mystery and murder know of the strange afterlife of the remarkable novel. Pictured: Bella, Thyrza Grey and Sybil Stamfordis in BBC’s The Pale Horse
When the company requested a reference from the Slough psychiatric clinic where Young had been an out-patient after leaving Broadmoor, the clinic forwarded a report by the unfortunate Dr Udwin.
‘Young had suffered a personality disorder necessitating hospitalisation throughout the whole of his adolescence,’ it stated.
‘He has made a full recovery and is fit for discharge.’ It made no mention of the fact that Young had poisoned members of his family, nor of his incarceration in Broadmoor.
Young immediately started making tea and coffee for his colleagues. But sugar wasn’t the only thing he added to the brews. Sickness swept through the firm, with almost 70 colleagues struck down.
Mistaken for a virus, it was nicknamed the Bovingdon Bug. When the head storeman, 59-year-old Bob Egle, died after several bouts of illness, followed — a few months later — by 60-year-old Fred Biggs, suspicions began to grow.
And, thanks to the Christie novel, a doctor working with Scotland Yard recognised the symptoms of thallium poisoning — which leads to organ failure.
At the same time, Young let slip to a colleague that his hobby was mixing toxic substances, and that was relayed to the police.
Young was arrested on November 21, 1971. Police found thallium in his pocket and a diary in his bedroom that noted every poisoning attempt, the amount he’d administered, their effects and, horrifyingly, whether he intended to let each victim live or die.
The plot turns on the almost undetectable effect of poisoning by thallium, a salt obtained from the rare heavy metal of the same name
During his trial, pathologist Professor Hugh Molesworth-Johnson revealed that The Pale Horse contained one of the few reliable descriptions of thallium poisoning outside a specialist text — but Young, truthfully or not, denied having read Christie’s novel.
He was sentenced to life, and this time there was no gullible medic on hand to secure his release. Eighteen years later, at the age of 43, he was found dead in his cell at Parkhurst prison, apparently from a heart attack.
Young is also suspected of having honed his craft behind bars at Broadmoor, extracting cyanide from the leaves of laurel trees that grew in the hospital grounds to poison staff and possibly kill his fellow inmate John Berridge.
Nearly three decades later, The Pale Horse was implicated in another killing: the so-called Mensa Murder.
Not long after receiving a threatening note, Florida waitress Peggy Carr, 41, fell gravely ill along with her husband, son and stepson. While the others recovered, Peggy died.
The murderer turned out to be their neighbour — a chemist and member of the high-IQ club Mensa called George Trepal, who had secreted the poison in Coca-Cola bottles. Police found a vial of thallium nitrate and books on poisons in his house — as well as a copy of Christie’s The Pale Horse.
But the book has saved at least one life, too. In 1977, a desperately ill one-year-old girl was flown from Qatar to London for medical treatment for a mystery illness.
Paediatricians could find nothing to account for her condition — and with her heart beating 200 times per minute, her blood pressure high and her breathing irregular, there seemed no hope.
A nurse, Marsha Maitland, overheard doctors talking about her symptoms, which included hair loss.
She was reading The Pale Horse at the time, and correctly suggested thallium poisoning (the toddler had eaten thallium-based pest-killer from under the sink). The child was treated just in time and made a full recovery.
Christie took her title from Chapter Eight of the Book of Revelation: ‘And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him . . .’ That chilling line resonates through this atmospheric book.
But in this one case, The Pale Horse carried not death, but life.