Short answers, pulled from the story.
Christie sold an estimated 300 million books during her lifetime. By the time of her death in January 1976, she was considered the best-selling novelist in history. Her total book sales have since surpassed two billion copies.
On the 3rd of December 1926, Christie vanished from her home in Sunningdale after a quarrel with her husband. Her car was found at Newlands Corner in Surrey; more than 1,000 police officers and 15,000 volunteers joined the search. She was located on the 14th of December 1926 at the Swan Hydropathic Hotel in Harrogate, Yorkshire, registered as "Mrs Tressa Neele". Two doctors diagnosed her with a genuine loss of memory, though opinions about the cause remain divided.
The Mousetrap opened at the Ambassadors Theatre in the West End of London on the 25th of November 1952 and holds the world record for the longest initial run. By September 2018, more than 27,500 performances had been given. The play was temporarily closed in March 2020 due to the coronavirus pandemic and reopened on the 17th of May 2021.
Christie's second husband was archaeologist Max Mallowan, whom she met in February 1930 during a visit to an excavation site in Iraq. Mallowan was 13 years her junior. They married in Edinburgh in September 1930, and the marriage lasted until Christie's death in 1976.
Christie worked as a hospital dispenser during both World Wars, first at the Town Hall Red Cross Hospital in Torquay, where she logged 3,400 hours between 1914 and 1918, and later at University College Hospital in London from 1941 to 1947. That experience gave her expert knowledge of arsenic, aconite, strychnine, digitalis, nicotine, thallium, and other toxic substances, which appeared as murder methods in more than half her novels.
And Then There Were None is Christie's best-selling individual novel, with approximately 100 million copies sold, making it one of the top-selling books of all time. In 2015 it was named the "World's Favourite Christie" in a vote sponsored by the author's estate.