Mr. Penumbra's 24-Hour Bookstore by Robin Sloan

After that, the book will fade, the way all books fade in your mind. But I hope you will remember this:A man walking fast down a dark lonely street. Quick steps and hard breathing, all wonder and need. A bell above a door and the tinkle it makes. A clerk and a ladder and warm golden light, and then: the right book exactly, at exactly the right time.

Robin Sloan's Mr. Penumbra's 24-Hour Bookstore was the perfect summer puzzler. It's part mystery (Da Vinci Code style except actually readable), part love letter to books, part critique of Silicon Valley.

Clay Jannon, our protagonist, has just lost his programming job and is adrift on the San Francisco job searching seas when he stumbles upon Mr. Penumbra's bookstore. He is hired to cover the night shift, and the more he learns about his employer and the store, the deeper he goes down the rabbit hole. Mr. Penumbra's regular clients never purchase books (they borrow and return large, cryptic volumes from the back of the store instead), and rather than making sales, Clay's job is to meticulously track the comings and goings of the clientele. Eventually, it becomes clear that the regulars are part of a secret society of sorts, working to solve an encoded puzzle, and Clay gets in on the action. He recruits his Silicon Valley cohort (programmers, billionaires, the usual...) to help, and antics ensue.

Neither Clay nor any of the other characters is particularly nuanced or interesting, but the puzzle is fun, and the members of Penumbra's entourage are endearingly odd. I was a little annoyed by the pervasiveness of start up culture and the looming spectre of Google; I have enough of both in real life and don't want them in my novels, but Sloan puts them down effectively enough to make it manageable. Also, as a result of their presence, there are a few descriptions of coding and programming that were enjoyable to read and vaguely (very vaguely) improved my knowledge of what coding actually is. Expanding horizons!

Overall, a quick, fun read with a twist of an ending.