I approached this with some wariness, as I saw other readers had tagged it as YA and my experiences in that genre has led me to expect tiresome teenaged angst and even more tiresome love triangles, but this was a pleasant surprise. The only connection with that genre I saw was the age of the primary female character. What I found instead was a good adventure fantasy with a well-developed world and rules of magic. The characters were fun, the world was fun, and the action was suitably violent and gory, even if the Antari trait of self-healing did rob some of the danger of its impact. I would have liked to see more well-developed villains, though. They were fairly two-dimensionally evil, simple baddies to be knocked down. We did get a little more depth to the opposing Antari, at least, so there was some investment in that character. The book is obviously the start of the series, but there is a satisfactory (enough) resolution to the books to events to allow this one to serve as a stand-alone.
I read this for the 2018 Halloween Bingo square Darkest London: any mystery, suspense, horror or supernatural book set in London. This book is set in several Londons in adjacent worlds, with one (not visited) literally called “Black London”.