I read cozy and historical mysteries, a bit of Paranormal/UF, and to mix it up, I read science and gardening books on occasion.
I bought and read this book almost 10 years ago - it was one of the first books I bought after moving to Australia, and I remember because I couldn't believe I was paying that much money for a book (prices here were astronomically high then - a mass market paperback was 20-25 dollars - where as now they only sit at a suborbital price). But this is one of those fancy books: clues like letters, newspapers, telegrams, etc. are mounted onto pages so that the reader can remove them from envelopes and play along. I'm such a sucker for these books. Like pop-ups, only people don't give you the side-eye for enjoying them without kids around.
The story purports to be real: a satchel found in the wall of a home being torn down in Philadelphia, present day, contained this letter from Dr. Watson, along with the clues. The reader is told at the beginning that no solution exists for the mystery and readers are invited to try to solve the very cold case.
It's really well done, really extraordinary, and the mystery itself is delightfully difficult. Everything is done more or less within the established canon timeline and remains faithful to Doyle's creations. No liberties are taken...not really:
I'm not sure if this is still in print or not, but if you're a Holmes fan and see it, take a look - it's one of the most faithful pastiches/homages I've yet found.