It could have been the plot from one of her bestselling mystery novels. 

Late on the evening of December 3, 1926, Agatha Christie walked up the stairs of her palatial English mansion, kissed her seven-year-old daughter goodnight, got in her car and drove away in the dark.

She had spent the day quarrelling with her husband, Colonel Archibald Christie, who had recently announced that he was in love with a younger woman and would soon be leaving his family behind. 

Instead, it was his wife who fled.

For the next 11 days, the most famous woman in the world was gone, sparking a nationwide manhunt that involved 1,000 police officers, 15,000 volunteers, bloodhounds and aeroplanes.

Fellow detective writer Sir Arthur Conan Doyle engaged the services of a psychic to try to track down his missing colleague. 

One newspaper offered a reward roughly equivalent to $A9,500. 

But then Archibald dropped a bombshell: Perhaps his wife was hiding in plain sight. 

“She may have disguised herself by altering the style of her hairdressing and by wearing glasses,” the Daily News tabloid wrote on December 11. 

At the time of her disappearance, Archibald had plenty to hide, and as suspicion began to fall on him, he panicked. 

“It is absolutely untrue to suggest that there was anything in the nature of a row or a tiff,” he told reporters.

“I strongly deprecate introducing any tittle-tattle into this matter.”

Finally, after 11 days gone, Agatha was found nearly 300 kilometres from her home. 

She had checked herself into a spa in Yorkshire under the name of her husband’s girlfriend and appeared to be confused about her identity.

“She does not know who she is,” Archibald told reporters. 

“She has suffered from the most complete loss of memory.”

From this strange episode, two conflicting narratives emerged. 

In one, Agatha was a woman in crisis, driven into a fugue state by the recent death of her mother, her collapsing marriage, and intense pressure from her publisher to deliver yet another bestseller. 

In the other, she was a shrewd manipulator — the original Gone Girl — who orchestrated her own whodunnit to humiliate Archibald for his philandering. 

For the rest of her life, she was reluctant to speak about her 11 missing days. 

She may have been the master of the genre, but the only Agatha Christie mystery that can never be solved is her own disappearance.  

A woman vanishes from the ‘unlucky house’  

On the surface of things, Agatha’s life looked perfect. 

Her sixth novel, The Murder of Roger Ackroyd, was published in mid-1926 and it was an instant hit, transforming the 36-year-old from a successful novelist into a global celebrity. 

She and Archibald, a dashing former military officer who was by then a successful businessman, had recently bought a 12-bedroom mansion in rural Berkshire. 

Many locals warned them it was an “unlucky house”, and everyone who lived there was eventually beset with romantic and financial woes. 

But they didn’t care. 

They wanted to raise their daughter Rosalind there. It was the perfect place for Agatha to write, and the local golf course was in walking distance so that Archibald could practice his swing. 

Perhaps they believed they could transform the house’s fortunes. 

But as 1926 drew to a close, the family’s luck was running out. 

Agatha’s mother died earlier in the year, and she had spent months at her childhood home sorting through her affairs. 

While she was away, Archibald met Nancy Neele, a woman 10 years their junior. 

By the time Agatha returned, her husband asked for a divorce so he could marry his new lover. 

The mood in the unlucky house grew dark. 

On the evening of December 3, Agatha called Archibald’s office to find out where he was, and learned that he was staying with friends for the weekend.

Among them? Ms Neele. 

As she wandered the halls of the mansion that was meant to their forever home, something broke inside of Agatha. 

She wrote three letters — one to her secretary, one to Archibald, and one to her brother-in-law.  

Leaving Rosalind in the care of household staff, Agatha packed some of her things in her car and drove away. 

The next morning, the car was found abandoned, crashed into a hedge with its front wheels dangling over a quarry. 

Her license and other belongings were on the front seat, but the author was nowhere to be found. 

The police search riddled with red herrings 

With tabloids constantly seeking scandal for their pages, news of Agatha’s disappearance spread around the world in a matter of days.

As with any good Agatha Christie mystery, the saga was riddled with missed clues and red herrings. 

While Archibald burned the letter from his wife and refused to tell police what was in it, his brother, Campbell Christie said Agatha had written to let him know she was going to a Yorkshire spa for a few days. 

But police were unconvinced by the letter and insisted the most important clue of all was the abandoned car. 

Believing she may have died or taken her life, a team of bloodhounds, as well as Agatha’s “favourite terrier”, were sent to scour nearby fields, but came up with nothing. 

Sir Arthur Conan Doyle, the creator of Sherlock Holmes, was a passionate believer in mysticism, fairies and ghosts.

He asked to borrow one of Agatha’s gloves, which he gave to a spirit medium so she could perform a seance. 

The medium insisted Agatha was a victim of “foul play” and she could be found at the bottom of a local lake, known as the Silent Pool. 

Police dragged the lake twice, but came up empty. 

With his wife missing and the tabloids scrutinising their lives, Archibald made a decision that he perhaps hoped would divert attention from himself and Ms Neele. 

He told reporters he believed his wife had staged her own disappearance to work out the mechanics of her next murder mystery. 

His claim took the intense interest in the case and turned it into a global obsession. 

“It is ridiculous,” her personal secretary told The New York Times when asked if the whole thing was a stunt.

With her face on the front page of newspapers and a substantial reward on the table, it seemed that every Briton was hunting for Agatha. 

Among them were the guests at the Harrogate Hydro, a luxury spa in England’s north. 

After days of drinking gin cocktails and dancing the charleston with a mystery woman, they realised Agatha Christie had been in their midst all along. 

‘Mrs Christie is a very elusive person’

On December 4, 1926, a woman arrived at the Harrogate Hydro in a taxi. 

She had no luggage with her, but staff reported that she seemed well and unharmed, and checked herself in under the name “Mrs Teresa Neele of Cape Town”. 

Mrs Neele enjoyed the spa treatments offered by the hotel, went shopping, and played billiards with the other guests. 

They too were abuzz with the mystery surrounding Agatha Christie, but Mrs Neele didn’t seem particularly interested when she saw the story in the newspapers. 

“Mrs Christie is a very elusive person,” a guest later recalled her saying.

After more than a week in her presence, guests and staff started to suspect Mrs Neele was, in fact, the missing author. 

A banjo player with the hotel’s band, the Happy Hydro Boys, reported his suspicions to police and claimed the $9,500 reward. 

The next day, Archibald and several police officers came to the hotel and found Agatha there. 

But she didn’t seem to recognise her husband, initially mistaking him for her brother. 

Agatha eventually remembered who she really was.

But she remained dazed and distressed as Archibald drove her away from the hotel and took her to her sister’s house to recover — and elude the press. 

“My wife’s memory is completely gone, and three years have dropped out of her life,” Archibald told reporters.

“She recognises me but does not recall our child Rosalind. It is a terrible tragedy.”

In 1926, there was little understanding of mental health, and almost no empathy for a woman who made her own money — particularly one who did so by spinning twisted tales about murder and intrigue. 

For the rest of her life, Agatha was haunted by accusations that she concocted this little drama, perhaps for publicity, or perhaps in an attempt to ruin Archibald’s life. 

‘Up until this moment I was Mrs Christie’ 

Agatha chose to speak only once about her missing 11 days. 

In 1928, two years after her disappearance, she was finally divorcing Archibald and concerned he might attempt to gain sole custody of their daughter. 

So she agreed to an interview with the Daily Mail in the hope of putting the saga behind her — and convincing the courts that she should be trusted with Rosalind’s care. 

“I just wanted my life to end,” she told the paper of the day she disappeared in 1926. 

“All that night I drove aimlessly about … In my mind there was the vague idea of ending everything.” 

She said she crashed her car and hit her head, and as she staggered down the wintry country roads looking for help, something strange happened. 

“Up to this moment I was Mrs Christie,” she said. 

The queen of crime fiction, always praised for her complex, believable characters, created a new identity for herself. 

“As Mrs Neele, I was very happy and contented,” she explained, insisting she truly believed herself to be a young woman who had just arrived in England from South Africa. 

She had only vague recollections of how she ended up at the spa in Yorkshire, but remembered that once she was there, she failed to recognise her own face in the papers. 

“At Harrogate, I read every day about Mrs Christie’s disappearance … I regarded her as having acted stupidly,” she said. 

Many historians and biographers believe Agatha’s story, and say she had all the hallmarks of having slipped into a fugue state. 

Those who have experienced these episodes of dissociative amnesia describe it as losing time.

They suddenly come back to themselves in an unfamiliar place with no memory of how they got there. They might not even remember their own name. 

“It’s time to do something radical,” biographer Lucy Worsley wrote in Agatha Christie: A Very Elusive Woman.

“To listen to what Christie says, to understand she had a range of experiences unhelpfully labelled as ‘loss of memory’, and, perhaps most importantly, when she says she was suffering, to believe her.” 

A week after their divorce, Archibald married Nancy Neele, while Agatha got custody of Rosalind and was allowed to keep the name upon which she built her career. 

With her marriage over, Agatha was adrift.

She decided to do what she loved most: She went on an adventure, travelling on the long-distance passenger service, the Orient Express, to the Middle East. 

The journey would inspire one of her most beloved novels, Murder on the Orient Express. 

And during her travels, she went to Iraq, where she met Max Mallowan, a handsome British archaeologist, who was 13 years her junior. 

They married six months later, and stayed together for the rest of her life. 

“I like living,” she wrote in her memoir.

“I have sometimes been wildly, despairingly, acutely miserable, racked with sorrow; but through it all I still know quite certainly that just to be alive is a grand thing.”