‘Mr. Penumbra’s 24-Hour Bookstore’ by Robin Sloan

There is something odd about the San Francisco bookstore where Clay Jannon clerks overnight.

From shelves filled floor-to-ceiling — the equivalent of three floors — Clay retrieves books not sold but loaned to members of a mysterious club. In addition to tracking each volume they take, he must document their appearance and behavior.

Inside the books, “a solid matrix of letters,” “an undifferentiated jumble.”

Clay stumbles ever deeper into a centuries-old pursuit to unlock a secret code, firmly placed in a modern world of online search, crowdsourcing and 3D-imaging.

From start to finish, Mr. Penumbra’s 24-Hour Bookstore was a delight to read. Written by Robin Sloan and published in 2012 by Picador, Mr. Penumbra’s 24-Hour Bookstore is a ninth- to 12th-grade selection for Oregon Battle of the Books.