The Atrocity Archives contains The Atrocity Archive and The Concrete Jungle, 2 short novels by Charles Stross. I had heard much good about this book, but found myself reading rather impatiently and not particularly enjoying the experience. They are a type of spy/thriller mixed with horror/science fiction, so I expected to love this. I was disappointed.
Stross' site describes the series (this is the 1st book of the series) this way:
Good news: magic is real. Bad news: it's a branch of mathematics—prove the right theorems, and entities in other dimensions may hear and, sometimes, do what you tell them to do. Worse news: this means that magic is best practiced by computer geeks—"applied computational demonologist" is a job description. Worst news: the extradimensional entities are the horrors that haunted the dreams of H. P. Lovecraft, and the Stars are Coming Right ...SF Signal calls it "very fun". SFReviews.net says, "Fiendishly clever and as bristling with deliciously subversive ideas as anything else he's written, this early work of Stross's shows it was no secret the man was going places." SF Site calls it "a very breezy, fun, and imaginative novel" and recommends it. Eyrie says, "...if the humor clicks for you, it's a thoroughly enjoyable tale."
But don't worry. Her Majesty's Government has a secret agency tasked with defending the realm from the scum of the multiverse. It's nick-named the Laundry by those hapless civil servants and computer geeks who work there, such as Bob Howard, who was drafted after his MSc project nearly landscaped Wolverhampton by accident. And they probably will save the universe ... if they can find their way out of committee hell first, and account for all the paperclips they're missing.