“Mr. Penumbra’s 24 Hour Bookstore,” was an odd novel that would appeal to computer nerds and bookworms. When Clay stumbles upon a job opening at a 24 hour bookstore, his need for cash motivates him to take the job. The same customers come in and borrow old, antique books, and after a while, Clay begins to suspect there is more going on than just reading. His background in computers prompts him to start tracing the books borrowed by each customer, and he inadvertently cracks a code that has baffled the store owner, Mr. Penumbra, for years. Suddenly thrust into a secret society of avid readers donning hooded robes and holding secret midnight book bindings, Clay works with his new girlfriend and Mr. Penumbra to create a computer system that will help the secret book society understand the larger code they have been trying to solve. The mystery was interesting and the plot moved along well. The author added a new twist to fiction by relying so heavily on computers, and I would almost categorize this novel as computer fiction. The writing was strong and the characters were believable. I especially liked that Clay’s childhood friend, who obtains fame and riches with the success of several websites, could be of assistance in helping the society. The novel was different, and to enjoy it, a reader would really need to be in the mood for a quirky science computer fiction novel.