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

The Great Recession relocated Clay Jannon from a web-design drone and into bookstore aisles. Customers never seem to buy - instead, they "check out" large, obscure volumes from strange corners of the store. He engineers an analysis of the clientele's behavior, seeking help from his talented friends. Approaching Mr. Penumbra, they discover the bookstore's secrets extend far beyond its walls.