The Daughter Who Poisoned Her Father's Tea

On this day, the 14th of August 1751, a respectable English lawyer named Francis Blandy died in terrible agony in the town of Henley-on-Thames. He had been slowly poisoned, over many weeks, with arsenic slipped into his food and his tea. The person administering that poison, day after day, was the person who loved him most, and whom he loved most in all the world: his daughter, Mary.

But Mary Blandy swore, to the very moment of her death, that she was innocent of murder. She insisted she had no idea the powder was poison. She believed, she said, that it was a magic love potion, sent by the man she adored, to make her father approve of their marriage. And nearly three hundred years later, we still cannot be entirely sure whether she was a cold‑blooded killer or the most tragically deceived woman in England.

Mary was the intelligent, well‑educated, much‑loved only daughter of Francis Blandy, a prosperous attorney. As she grew older without marrying, her doting father did something that would prove fatal: to attract a good husband, he made it known that she would come with an enormous dowry — ten thousand pounds, a fortune in the mid‑18th century. That fortune drew in exactly the wrong kind of man.

His name was Captain William Henry Cranstoun, the son of a Scottish nobleman. He swept Mary off her feet. There was just one serious problem: Cranstoun was already married, with a wife and children in Scotland. He was a fraud and a fortune‑hunter, chasing Mary’s dowry. When Francis Blandy discovered his daughter’s suitor already had a wife, he was appalled. He broke off the match and sent Cranstoun away. It should have ended there. Instead, it was the beginning of a tragedy.

The Horror

From a distance, Cranstoun was not willing to lose the dowry. He hatched a plan and used Mary’s love as the weapon.

He sent her a quantity of white powder and told her a lie: that it was a special love philtre, a magic potion. If she would secretly sprinkle it into her father’s food and drink, he told her, it would soften his heart and make him bless their marriage. Mary, besotted and desperate, did as she was told. Over months, she stirred the powder into her father’s tea and gruel.

It was not a love potion. It was arsenic. As Mary kept administering it, believing she was slowly winning her father’s blessing, she was in fact slowly killing him. Francis Blandy began to suffer terribly: violent stomach pains, sickness, a slow, agonising decline.

One of the most heartbreaking details is that he came to realise he was being poisoned — and that his own daughter was involved. Accounts from the time say he believed Cranstoun had deceived her and forgave Mary, seeing her as a victim of manipulation rather than a deliberate murderer. He died on 14 August 1751.

The Modern Relic

The law, however, was not so forgiving, and the evidence that emerged cut both ways — which is exactly why the case still haunts people.

There were things that looked very bad for Mary. The servants had grown suspicious as their master sickened. One found mysterious white powder in a pan Mary had used to prepare his food. When her father died and Mary realised suspicion was closing in, she panicked and tried to destroy evidence, throwing remaining powder and Cranstoun’s incriminating letters into the fire. A quick‑thinking servant rescued some of it and handed it over.

Worst of all, a servant testified to a chilling remark she claimed to have heard Mary say: “Who would not send an old father to hell for £10,000?” Other witnesses recalled Mary admitting she “knew the consequence” of what she was doing. The prosecution asked: how could a woman repeatedly dose her father over months, watching him suffer and waste away, and still claim she thought she was giving him a harmless love charm?

Her trial at the Oxford Assizes in March 1752 became a national sensation. It also became a milestone in forensic history. Dr Anthony Addington, her father’s physician, performed tests on the recovered powder and on decoctions made from the gruel, comparing them with white arsenic and presenting his results to the jury — one of the first times chemical evidence in a poisoning case was formally recorded in an English court. The jury listened to it all and found Mary Blandy guilty of murder.

She was sentenced to hang. Mary went to her death still insisting, calmly and steadfastly, that she had never meant to harm her father and had truly believed the powder was a love potion. On Easter Monday, 6 April 1752, she was led to the scaffold near Oxford Castle before a huge crowd.

There she spoke the words that have echoed ever since as one of the most human final requests on record. Modest to the last, afraid her skirts would ride up indecently when she dropped, she turned to the executioner and said: “For the sake of decency, gentlemen, do not hang me too high.” Then she died.

As for Cranstoun — the man who sent the poison and manipulated a loving daughter into killing her father — he escaped English justice, fleeing abroad. But he did not escape his fate. He died later that year in France or Flanders, reportedly in poverty and illness. Public sympathy was strong for Mary Blandy. There was none for him.

And so the question that hung over the scaffold at Oxford hangs there still. Was Mary Blandy a murderess who knowingly poisoned her father for love and money, hiding behind a fairy tale about a philtre? Or was she the ultimate victim, a naive and besotted woman genuinely tricked by a manipulative liar into becoming the unwitting instrument of her father’s death?

The evidence points both ways. She unquestionably administered the arsenic; she unquestionably tried to destroy incriminating powder and letters; witnesses claimed she made damning remarks. Yet her own account, some contemporary observers, and her father’s reported forgiveness portray her as Cranstoun’s dupe, caught between love, superstition and a ruthless con‑man.

The law did not believe her and hanged her. Nearly three centuries later, historians still argue — and we are left to wonder about the woman who fed poison to the man who loved her most, and swore with her dying breath that she never knew.

← Back to the archive