She's the best-selling novelist of all time, and created two of the most popular detectives in history, Miss Marple and Hercule Poirot.

But writer Agatha Christie starred in her own real-life mystery, and for more than 90 years her fans have struggled to figure out what happened during the 11 days she totally disappeared.

The novelist's long career had just begun in 1926, when Christie had six novels under her belt and had already become a household name on both sides of the Atlantic. But Christie's husband Archie asked her for a divorce, revealing he had fallen in love with another woman while on Agatha's latest book tour.

Of course the writer was upset, and the couple got into a fight on the night of December 3, before Archie left the house in a huff. He would spend the weekend with his mistress.

That night, Christie kissed her sleeping daughter  Rosalind and left their house in Sunningdale, England just before 10 p.m. In a note to her secretary, Christie explained that she was leaving for Yorkshire.

But the next day her car was found abandoned by the cliff of a nearby quarry.  

Inside the car was Christie's expired driver's license and some of her clothes. The famous writer's disappearance was soon national news, with a newspaper offering the equivalent of $8,000 for information on her whereabouts.

Over the following days Christie's case made the front page of The New York Times, as 1,000 police officers, 15,000 volunteers and a team of airplane pilots searched for her - or her body.

Sir. Arthur Conan Doyle, the creator of Sherlock Holmes, even invited celebrity psychic Dorothy Sayers to investigate Christie's home for supernatural clues. Sadly, she didn't find anything.

Eleven days after vanishing without a trace, Christie finally turned up in a very unlikely place: a nearby hotel. She had registered as Mrs. Teresa Neele - the name of Archie's mistress - and had signed that she was from South Africa.

The author claimed she had no memory of her disappearance or how she arrived at the hotel, and left police (and her fans) to try and connect the dots.

Now, after 90 years of guessing, Christie experts have a number of theories about the disappearance.

Christie stayed quiet about her 11-day vanishing act for the rest of her career, and her biography does not mention that time at all.

At the time, most people assumed that Christie had planned her disappearance as a publicity stunt for her novels, a real-life "whodoneit" that would be right at home in one of her detective stories. Some fans guessed she had been genuinely trying to frame her husband Archie for her murder.

The 1979 film Agatha follows this theory, with Christie (played by Vanessa Redgrave) trying to commit suicide while framing Archie (Timothy Dalton) for her murder. Christie's heirs unsuccessfully sued to keep the film out of theaters.

A recent biographer, Andrew Norman, believes that a distressed Christie was trying to commit suicide when things went wrong and spiraled out of control.

He points out that in one of Christie's romance novels (written under the pen name Mary Westmacott) a character named "Celia" considered a suicide attempt but the shame convinced her not to follow through.

In a Daily Mail interview from 1928, Christie also discussed a failed suicide attempt near a quarry:

There came into my mind the thought of driving into it. However, as my daughter was with me in the car, I dismissed the idea at once. That night I felt terribly miserable. I felt that I go on no longer. I left home that night in a state of high nervous strain with the intention of doing something desperate.

When I reached a point on the road which I thought was near the quarry, I turned the car off the road down the hill towards it.  "I left the wheel and let the car run. The car struck something with a jerk and pulled up suddenly. I was flung against the steering wheel, and my head hit something. Up to this moment I was Mrs Christie.

Another writer who examined the Christie mystery, novelist Andre Wilson, proposed that Christie suffered a car accident like the one she described in 1926, causing her memory loss.

Others have suggested that the stress of the divorce drove Christie into a kind of temporary amnesia known as a "fugue state." The author's mother had also died the same year Archie divorced her, and Christie spoke openly about suffering weight loss and insomnia caused by the stress of losing her.

Christie and Archie divorced in 1928, and the novelist never fully explained the cause of her disappearance. That's just like a great mystery writer: she took the solution to her best case to the grave.

What do you think caused her disappearance?

[H/T: History Extra, Telegraph]