A better title might have been "Call of Cthulhubert".

Bob Howard is a desk jockey at the secretive British agency called "The Laundry". Between bureaucratic scuffles, snippy secretaries, and bosses who believe in only using typewriters to hammer out important documents, he occasionally stumbles upon plots to unleash eldrich horrors onto the world through the use of advanced mathematics. The Alan Turing/H.P. Lovecraft paper "Phase Conjugate Grammars for Extra-Dimensional Summoning" kind of turned everything upside down, and ever since, it's been a squirrely kind of touch-and-go, with government agents clamping down on anybody who seems to be on the verge of rediscovering the technology.

The writing is pretty good for a second book (his first book was "Singularity Sky", and there's a lot of similarity in style) but if you've read "Accelerando" and are backfilling your collection, don't expect him to write on the same level. To be honest, only "Iron Sunrise" has approached the quality of writing that Stross demonstrated in "Accelerando", and even that was just "approached", not "matched" in my opinion. Still, a fun little read and a nice diversion when working for a bunch of cloistered bureaucrats drives you up the wall.