This book was a LOT of fun. I love literary puzzles; they are one of the few practical uses of a B.A. in English Literature. I already knew the identity of the never-named "old man" in this story, and so does anyone who reads book reviews, so I’m not giving much away when I say that the detective in this story is Sherlock Holmes; a very aged Sherlock Holmes, coming out of deep retirement to solve a murder, and find a missing parrot who may (or may not) hold the key to some kind of Nazi encryption system. But other puzzles are embedded in the story, along with other coded references to Holmes's earlier exploits; it's fun picking them out. The revelation of the encryption mystery is also done quite subtly--it's possible to miss it if you aren't paying attention.
I'm kind of interested in the spate of books that expand the Holmes universe. I have read a few of the Laurie King mysteries about Holmes and his wife, Mary Russell. They are okay, but not my favorites; I never really got over the ick factor of the huge difference in their ages. Chabon's Holmes is more interesting and in worse shape than King's. Other recent releases include A Slight Trick of the Mind, by Mitch Cullen, The Italian Secretary, by Caleb Carr, and Arthur and George, by Julian Barnes, which is about not Holmes, but Sir Arthur Conan Doyle. I haven't read any of these, but would like to.