Please note: I don't review to provide synopses, I review to share a purely visceral reaction to books and perhaps answer some of the questions I ask when I'm contemplating investing time and money into a book.
If you like the Laundry series, you'll like this short. It's a very quick read and treads well worn ground, but all the things I like about the Laundry are in abundance: sly digs at English culture, comically overdrawn computer science and good ol' fashioned whatdunnit in the vein of classic Dr. Who.The references to the eldritch gods and Crowley are like a fractal tesseract and provide the real meat of the story.
For people not familiar with The Laundry, this would work as a standalone. There's enough context provided to explain who the players and are and what they're doing, and the voicing, cadence etc are all exemplary of the series. For people familiar with the series, reading this out of order (like I have) didn't detract my enjoyment.