Global conspiracy, complex code-breaking, high-tech data visualization, young love, the secret to eternal life. Mostly in a hole-in-the-wall San Francisco bookstore.

Clay Jannon tells how serendipity, sheer curiosity, and the ability to climb a ladder like a monkey has sent him from Web Drone to night shift at Mr. Penumbra’s 24-Hour Bookstore. After just a few days on the job, Clay realizes just how curious this store is.

A few customers come in repeatedly without buying anything. Instead they “check out” obscure volumes from strange corners of the store. All runs according to some elaborate, long-standing arrangement with the gnomic Mr. Penumbra. The store must be a front for something larger, Clay concludes.

He embarks on a complex analysis of the customers’ behavior and ropes in friends to help. Once they bring their findings to Mr. Penumbra, it turns out the secrets extend far outside the walls of the bookstore. A quest to New York City dips in a world conspiracy for eternal life. The current of romance pulls Clay onward.