Everything we need to know is worked efficiently into the story, which is allowed to get on at a cracking pace. Mills doesn't waste much time trying to justify the existence of these creatures - you just suspend any disbelief and get on with it - and since most of the characters themselves belong to the various groups, there's no getting bogged down in an ordinary human finding out and learning about them. Most types have their own clan structure, too, and various political shenanigans are hinted at both within and between these groups, giving the preternatural world a richness and solidity. The manner in which demons recruit allows for a lot of character intrigue, as well as being particularly unpleasant (relatively so - there's no real gore in this, yet neither is there a feeling of punches being pulled). Some breed true, some recruit from the human population, some are immortal, some not. The various types of preternaturals - demons, sentinels (descended from angels, according to their own lore), vampires, witches etc - are extremely well set up. In fact, everything in the book seems to fall cleanly and naturally out of the starting conditions, which is that there are various types of 'preternaturals' living in human society, hidden in plain sight, prevented from open warfare by a Covenant that is fraying badly and a newly 'turned' half-demon who decides to go on the run, at great risk to her life, because she refuses to make the kill that will make her a full member of her pack. It's a very tightly and twistingly plotted, well-written story, packed full of tension, intrigue and action, with teenage characters you can get behind and who aren't hormoaning all the time or getting into pointless love-triangle diversions to spice things up. I read this as an ARC, and didn't take long about it.

Heart Blade by Juliana Spink Mills