…and, yes, it seems to be by Sir Arthur Conan Doyle himself, who had written it for a charitable cause! According to the UK “Telegraph”:
“Walter Elliot, 80, found the 1,300-word tale starring the famous detective in a collection of short stories written for a local bazaar.”
Personally, I especially like the fact that they (as in “The Telegraph” and the lucky finder Mr. Elliot) provide the opportunity to read it for free.
[Please see update]