The copy is a first edition, first issue from 1890, retaining its original publisher's red cloth binding with gilt lettering on the upper cover and spine. A bookplate inside reveals it once belonged to James Burgess Boote of Gwernaffel, Knighton, who served as High Sheriff of Radnorshire - adding another intriguing chapter to its story.
Tom Cotton, manager of the Oxfam bookshop in Shrewsbury, said: "The book was donated by a very generous, regular donor who had always been delighted to see his books valued highly and placed in our cabinets.
"Initially, I could tell the book was special - it was an early Sherlock Holmes story.
“However, when it comes to appraising antiquarian books, I do not have the power of deduction like Sherlock Holmes - I'm more of a Mrs Hudson! Determining the value was a real group effort. I had my own Baker Street Irregulars: my volunteers, the Oxfam Book Development Team, my Area Manager, and even a close friend of my Area Manager. To prevent the book falling into the Reichenbach Falls of an Oxfam backroom, I used their skills to uncover a rare find!"