I really hate giving any book a bad review, but I felt in this case I could do no other. To say the “mystery” was thin and obvious is undoubtedly being kind. The idea wasn’t a bad one, but the execution was really poorly handled. The only motivation I could see for the principle characters working it out was a kind of thoughtless curiosity.

https://www.amazon.com/Study-Stone-British-Mystery-Devonshire-ebook/dp/B07S1GTNV7