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In page The Mystery of the Blue Train:

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The particulars related to the dedication are these. Christie's mother died on 5 April;[3] also referenced are the breakdown of her marriage to Archibald Christie, and her famous ten-day disappearance in December that year.[citation needed] These were events which disturbed her for the remainder of her life,[4] and Christie learned that people she expected to be allies in her time of need turned away from her.[citation needed] One person who didn't was Charlotte Fisher (born c. 1901 – died 1976), who had been employed by Christie in 1924 as both her own secretary and as a governess to her daughter Rosalind.[2]: 339f