The Laundry Files: Book 7. This is a soft reboot, so you can start here. A better start is at the beginning of the series with the Atrocity Archive, or with the short story the Concrete Jungle (which has minor spoilers for the Atrocity Archive, but is a stronger introduction).
I did not like the last laundry book, the Annihilation Score. The previous laundry files entries were an ungodly hybrid of espionage, Cthulhu, and bureaucracy; a series where a character was as likely to save the world from tentacled horrors as be disciplined for not filling out leave forms correctly. The last entry was a logical continuation, but swapped the espionage for super-heroics, and in doing so, lost some of its scrappy charm.
The Nightmare stacks is a return to form, indeed, it feels somewhat like a soft reboot. Picking up a character from the Rhesus Chart, we have an over-competent desk jockey getting their first outing in the field, just like the first book. As befitting the 7th book in the series however, the stakes are raised, with the hero a vampire magician, and the threat a full blown fairy invasion.
All of the best (and worst) of Stross is on display here: the premise is treated absolutely straight, thinking through what the (post?) modern British army would do against a magic army of elves, dragons, and wizards, but sometimes the detail can detract from the story, such as a segment on basilisks petrifying the paint on aircraft. Most importantly it’s back in espionage mode, this time cold war spies, counterspies and honey traps.
A return to form from a series I really like.1