The October Man by Ben Aaronovitch

This is a novella that is part of the Rivers of London series that takes the action to Germany and focuses on a new character - Investigator Tobias Winter of the "Abteilung komplexe und diffuse Angelegenheiten" (aka the KDA or roughly translated as weird bollocks) - the German equivalent of the Folly in the main series. He is accompanied by Vanessa Sommer - a regular cop who is introduced to the world of river goddesses and malevolent supernatural forces when a dead body is found in a vineyard in mysterious and gruesome circumstances.

I enjoyed the different take on a supernatural police procedural from a German perspective, and the Moselle valley setting makes for an interesting change of setting too. It's a fairly short read, but sets up the mystery and resolves it in a satisfying way without feeling rushed. I'd definitely like to read more stories featuring Winter and Sommer, hopefully crossing over with the main series.