The affair began in the summer of 1917. Ten-year-old Frances Griffiths was on holiday in the village of Cottingley near Bradford. Her favourite game was messing about in the local beck. When she returned home wet, she provoked her mother’s favourite moan. What, she demanded, did the girl do there that was so fascinating? “Play with fairies” was the child’s astonishing answer.

Even more astonishing were the photographs that her 16-year-old cousin Elsie Wright took soon after. There was Frances in the woods with five fairies dancing in front of her. Then there was Frances with a gnome on the hem of her dress. In total, there were five magical Cottingley images.

These were spiritual times. Seances were popular, and Frances’s mother attended a Theosophists’ meeting, where she mentioned the pictures. News spread and in 1920 Conan Doyle heard about them. In later life the creator of that most intellectual of detectives had become a passionate spiritualist, even writing a book called The Coming of Fairies. He obtained the photographs for publication, declared them genuine and stuck to his guns in the face of considerable scoffing.

Elsie did not confess until 1983, when her “fairies” were found in a 1915 children’s anthology. Only then did the 83-year-old woman admit she had copied the pictures, mounted them on cardboard, and fixed them on bushes with hat-pins.

Conan Doyle had succumbed to middle-class prejudice, with a dash of sexism.

He had refused to believe that “two children of the artisan class” were capable of such “photographic tricks”. But the creator of the Cottingley fairies was actually a young woman and a trained artist who had once worked as a photographer’s assistant.

But then maybe, as Holmes said to Watson, the fair sex was not his department.