Mr. Penumbra's 24-hour Book Store by Robin Sloan

Clay Jannon had a successful life in the tech world of San Francisco but when that ends, the only job he can find is the 11 to 7 shift in a very strange all night book store.  There is a regular collection of books for sale - mostly science fiction - but they seem to be beside the point.  The rare customers that visit are mostly looking for very specific books located by coordinates in the dark high shelves in the restricted back of the bookstore.  Enter Kat Potente, techno geek who works at Google, and instant love of Clay's life.  Soon the two of them are drawn into a mysterious world of historical printing, secret societies, and the use of some way cool technogear to stop a possible murder.  It is great fun and I loved that Kat isn't the least bit hesitant to show off her brain guns.