Chem Dog belongs to the Warhammer 40,000 universe, which is a genre in itself before it is a setting: a far future of endless war, where the humans are frequently as frightening as whatever they are fighting. The novel picks one of the least glamorous corners of it, a penal legion, and follows a newly posted commissar sent out with a kill team into ork-held ground.
Our shelving lists it under science fiction and fantasy, and the science fiction half is the honest one. Callum Davis is an author we know through this book and this universe alone, and the writing suggests somebody comfortable with the grimmer register the setting demands rather than a tourist visiting it.