Mr Penumbra’s 24-Hour Bookstore is a smart, playful romp that begins in a musty secondhand bookstore in San Francisco then weaves through time and place, with stops at a book-worshipping cult in ancient Egypt (probably imagined by the author), a cavernous library hidden underneath 5th Avenue in New York (possibly imagined by the author), and the Google campus in California (not). Our hero, a young …