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

Inside, the pages were wide and gray, filled with dark handwriting. There were sketches, too: thumbnail portraits of bearded men, tight geometric doodles. Penumbra gave the pages a heave and found the place about halfway through, marked with an ivory bookmark, where the writing ran out. "You will note names, times, and titles," he said, tapping the page," but also, as I said, manner and appearance. We keep a record for every member, and for every customer who might yet become a member, in order to track their work." He paused, then added, "Some of them are working very hard indeed."