Bob Howard, SysAdmin and Occult Ops. field operative for The Laundry, continues to have an interesting life. Here, his destiny is entangled with a demon, and he's charged with stopping a billionaire megalomaniac from awakening the Old Ones at the bottom of the ocean, and hastening the onset of CASE NIGHTMARE GREEN - and all without blowing his expense account. If you've read The Atrocity Archives, you'll know some of what I mean; if not, I haven't spoiled anything for you and you have some pleasantly diverting reading to do.
Stross's writing style is very accomodating without being patronisingly simple, and I read through this over the course of a few day's worth of train trips. Bob, his main character, has an amusing inner monologue which portrays the clear contempt Stross has for modern executive corporate work practises (and handily serves as a narrative since the book is basically a first-person account), and somewhat oddly this is also a book about how mathematics and physics are actually the basis of demonology (the "demons" in these books are actually extra-dimensional aliens, albeit highly dangerous ones who aren't always sentient). The plot begins to creak a bit once the major plot exposition is underway around the final third of the book, and although this strays into sci-fiction horror, it actually begins to become slightly ridiculous rather than engaging - slightly "schlock", if you ask me. I didn't like where the "James Bond" theme was going, and it kept going right up till the afterword.
The previous novel, The Atrocity Archives (actually a collection of related short stories), is the better bet here, in my opinion. The Jennifer Morgue isn't a bad book, and I enjoyed reading it - but the prequel is better, I think.