Louise would have certainly been appalled by the treatment that Mary and Kingsley suffered at the hands of their father and his new wife. The two children were separated when they most needed one another. Kingsley was sent to Eton for his schooling, Mary to Dresden for singing lessons. Mary soon suspected that she would not be allowed to see Kingsley, even at Christmas. Two of her early letters to Kingsley reflect her anger, disappointment, and pain.
My boy—if I don't come home for Xmas there will be words—for the girls I travelled out with are returning for 3 weeks and coming back again after. [… there] is no reason why I shouldn't, unless they want to clear us both out […] and have it to themselves for Xmas. We are a bit of a mistake now. But never mind old chap, we'll stand together whatever happens.
When Mary pressed Arthur on the matter, he told her that he did not expect to see her for another nine months. He accused her of being weak for even asking to come home. She wrote again to Kingsley.
I can't think why my father is so hard—I have not had one gentle word, or sign of love from him since Mother died. One would have thought it would be otherwise. But no—life has all gone to make him a very hard man.
In a subsequent letter, she painfully accepted that she and Kingsley were no longer wanted.
It's for all the world as if they didn't care. […] But at least they might hide it more decently.
Kingsley too was disappointed by Christmas. He had been sent to an aunt's home for the holiday season and allowed home for Christmas itself, but made to feel unwelcome. Mary exchanged "words" with Jean over the matter, and wrote again to Kingsley.
I feel alternately angry and sad for you. I consider the least Daddy and Jean could have done, considering they denied you me—your natural companion—was to have made you as at home and happy in the New Life as possible. And in neglecting you like that, I consider they have let slip a very important duty. I'm disappointed in both of them.
Arthur and Jean's treatment of Louise's children was simply cruel without cause. Mary, for example, had arranged to have Kingsley visit her in Dresden, and she hoped also to travel to Berlin to see an opera that she had been studying. Having no money of her own, she turned to her father, by then one of the richest men in England, for the £20 necessary. He sent her a £10 check and a note, claiming that he could not afford to pay for both the opera and Kingsley's trip to Dresden. He left Mary to choose one or the other.
Intrepid Mary somehow managed both. While Kingsley was in Germany, he received a letter from Arthur berating him for a slight against Jean. Jean had apparently given Kingsley flowers or left flowers in his room, and he had not properly thanked her. In his groveling reply, Kingsley apologized profusely. He asked Arthur and Jean to provide him with a list of all his faults, so that he could improve on them.
Kingsley joined the military, suffered a neck wound during the battle of the Somme, and died of flu just a few days before the end of the war. He died unwed and without children. Only Mary could extend Louise's bloodline. She spent her life alone, however, both figuratively and literally. Though Arthur had arranged for his sisters to interact with potential suitors, neither Arthur nor Jean ever made the same effort for Mary. Instead, they kept her financially dependent on them. As Jean bore Arthur two more sons and another daughter, Mary became only more isolated.
When the couple toured Australia and New Zealand, along with their three shared biological children, they left Mary behind, alone. They forsook her again when they visited America, twice, then again when they traveled the length of Africa.
We learn from Mary’s writings that both Jean and Arthur cautioned her against marriage. Regarding Arthur's advice, she wrote:
He didn't concur with the Victorian view that women should marry at all costs—for he thought the unmarried woman, with her freedom, was a whole lot happier than a woman married to the wrong man and, he added, "The worst of it is, the poor things can never tell till they have married the chap!"
Jean insisted that a man should never marry a woman of equal intelligence, so Mary should wait for someone brighter than she was. This she did, it would seem, living a quiet, lonely, unremarkable life, trying to please. She followed her father as he turned towards the paranormal, and she worked in the bookstore that he opened to promote the spiritualist cause. Later in her life, she recalled fondly her talks with him, noting that he had a lovely mind and the capacity to see many points of view. For some time after his demise, she participated in séances longing to speak with him again.
Just weeks before his death, Arthur (presumably with Jean’s involvement) drew up the will that would be the final affront to Louise and her children. He bequeathed Mary some cash, only a portion of the farm property that had previously belonged to Louise, and an £8000 war bond that proved worthless. He excluded Mary from the real wealth of his estate, the copyright to his writings. That asset he divided in two, bequeathing half to Jean and half to be split among the three children from her womb. Mary’s much earlier observation to Kingsley, that "in all future dealings it is Jean and not Daddy with whom I shall have to reckon with," proved prescient.
Mary died, unmarried and childless, on 12 June 1976, whereupon the bloodline of Louise Conan Doyle came to an end.
None of Arthur's more recent biographers doubt that family papers were cleansed of documents relating to Louise. Of the purge, the editors of A Life in Letters wrote: “Very few letters have survived from 1885 and the next two years, driving Conan Doyle's biographers to other sources for some momentous things happening in his life.”
Andrew Lycett addressed the document dispute between two of the three children born to Jean and Arthur.
Feeling the need to defend himself against suggestion that he had been hoarding jointly owned material, [Adrian] told [his sister] Jean that he had been charged by their mother to burn two boxes of her love letters from their father. On the day of her death he had gone to Windlesham and though aware of the sacrilege, had carried out her instructions.
Lycett himself witnessed the continued culling of papers from family archives.
Imagine my astonishment when on one of my early visits to the British Library's manuscripts room I found Charles Foley at a nearby table. I learned that he was going through all the letters Dame Jean [the younger Jean] had left to the Library with the intention of withdrawing significant numbers. He was apparently allowed to do this under article 6 of Dame Jean's will. […] When I asked Foley about his criteria for selection, he declined to answer, saying this was a matter for him and his co-executor. However, I acquired a list of seventy-five items Foley intended to remove from the library. Ninety percent were letters from Conan Doyle to his mother.
Russell Miller, author of The Adventures of Conan Doyle (2008), speculates thusly about the motive for destroying and suppressing the documents:
[N]one of Touie's letters survive—it is possible they were destroyed after Conan Doyle's death because Jean wanted to be seen as the great, unrivalled, love of his life.
But perhaps there was something even more substantial in those letters, something that would materially threaten Arthur’s legacy and the value of the family’s inheritance.