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

Looking for any work, laid-off San Francisco web designer Clay Jannon answers an ad for a clerk at Mr. Penumbra’s 24-hour bookstore.  Looking for a normal desk and a normal boss, he finds Penumbra who, to say the least, is a bit odd.  Looking to keep the job, Clay follows the rules about keeping meticulous records of who comes into the store and what books they ask for.  Especially those that request them from the “back” of the store.  Looking to satisfy his curiosity, Clay opens one of the requested books, only to find it written entirely in code.  Looking for more answers, Clay confronts Penumbra.  Looking for an apprentice in a secret society, Penumbra explains his motivations.  Looking to solve the mystery of immortality, Clay and his companions travel to New York and the headquarters of the secret society, only to discover that they will never look at anything the same way again.  A great, mysterious read.