According to the Guinness Book of World Records, Christie is the best-selling writer of books of all time and, with William Shakespeare, the best-selling author of any kind. Only the Bible has sold more than her roughly four billion copies of novels. According to UNESCO, Christie is the most translated individual author, with only the collective corporate works of Walt Disney Productions surpassing her. Her books have been translated into at least 103 languages.
Christie's stage play The Mousetrap holds the record for the longest initial run: it opened at the Ambassadors Theatre in London on 25 November 1952 and as of 2010 is still running after more than 23,000 performances. In 1955, Christie was the first recipient of the Mystery Writers of America's highest honour, the Grand Master Award, and in the same year Witness for the Prosecution was given an Edgar Award by the MWA for Best Play. Most of her books and short stories have been filmed, some many times over (Murder on the Orient Express, Death on the Nile and 4.50 From Paddington for instance), and many have been adapted for television, radio, video games and comics.
In 1968, Booker Books, a subsidiary of the agri-industrial conglomerate Booker-McConnell, bought a 51 percent stake in Agatha Christie Limited, the private company that Christie had set up for tax purposes. Booker later increased its stake to 64 percent. In 1998, Booker sold its shares to Chorion, a company whose portfolio also includes the literary estates of Enid Blyton and Dennis Wheatley.
In 2004, a 5,000-word story entitled The Incident of the Dog's Ball was found in the attic of the author's daughter. This story was the original version of the novel Dumb Witness. It was published in Britain in September 2009 in John Curran's Agatha Christie's Secret Notebooks: Fifty Years Of Mysteries, alongside another newly discovered Poirot story called The Capture of Cerberus (a story with the same title, but a different plot, to that published in The Labours Of Hercules). On November 10, 2009, Reuters announced that The Incident of the Dog's Ball will be published by The Strand Magazine.
In late 1926, Agatha's husband, Archie, revealed that he was in love with another woman, Nancy Neele, and wanted a divorce. On December 8, 1926, the couple quarreled, and Archie Christie left their house Styles in Sunningdale, Berkshire, to spend the weekend with his mistress at Godalming, Surrey. That same evening Agatha disappeared from her home, leaving behind a letter for her secretary saying that she was going to Yorkshire. Her disappearance caused an outcry from the public, many of whom were admirers of her novels. Despite a massive manhunt, she was not found for eleven days.
On December 19, 1926, Agatha was identified as a guest at the Swan Hydropathic Hotel (now the Old Swan Hotel) in Harrogate, Yorkshire, where she was registered as 'Mrs Teresa Neele' from Cape Town. Agatha gave no account of her disappearance. Although two doctors had diagnosed her as suffering from psychogenic fugue, opinion remains divided as to the reasons for her disappearance. One suggestion is that she had suffered a nervous breakdown brought about by a natural propensity for depression, exacerbated by her mother's death earlier that year and the discovery of her husband's infidelity. Public reaction at the time was largely negative, with many believing it a publicity stunt while others speculated she was trying to make the police believe her husband had killed her.
To honour her many literary works, she was appointed Commander of the Order of the British Empire in the 1956 New Year Honours. The next year, she became the President of the Detection Club. In the 1971 New Year Honours she was promoted Dame Commander of the Order of the British Empire, three years after her husband had been knighted for his archeological work in 1968. They were one of the few married couples where both partners were honoured in their own right. From 1968, due to her husband's knighthood, Christie could also be styled as Lady Agatha Mallowan, or simply Lady Mallowan.
From 1971 to 1974, Christie's health began to fail, although she continued to write. Recently, using experimental, computerised, textual tools of analysis, Canadian researchers have suggested that Christie may have begun to suffer from Alzheimer's disease or other dementia. In 1975, sensing her increasing weakness, Christie signed over the rights of her most successful play, The Mousetrap, to her grandson.
Agatha Christie died on January 12, 1976 at age 85 from natural causes at her Winterbrook House in the north of Cholsey parish, adjoining Wallingford in Oxfordshire (formerly part of Berkshire). She is buried in the nearby churchyard of St Mary's, Cholsey.
Christie's only child, Rosalind Margaret Hicks, died, also aged 85, on October 28, 2004 from natural causes in Torbay, Devon. Christie's grandson, Mathew Prichard, was heir to the copyright to some of his grandmother's literary work (including The Mousetrap) and is still associated with Agatha Christie Limited.