A good backstory to several of the Slow Horses characters. You might get the most enjoyment of this if you've read up to Spook Street [bookwyrm.social/book/201447/s/spook-street] first, but it does stand alone. I've noted before that Berlin is important to the Jackson Lamb backstory and that "Atomic Blonde" is a good companion for that reason. Herron fleshes that out a lot more in this.