I love Rachel Caine's Weather Warden series - well, at least the first four or five books that I have read - but hadn't read any of her more recent offerings. When I picked up Unknown, I assumed it was a different series from the Weather Wardens. Indeed it is, but it shares many links to that previous series and mentions many of the same characters.

I haven't read the first book the Outcast Season (Undone), but that doesn't appear to matter too much. I think I'd have found this book much more confusing if I didn't already know the basic structure of the Weather Warden series and some of its characters. Unknown is rather darker and less character-driven than the others, focusing on Cassiel, a Djinn who is now something approaching a human - and who, with Earth Warden Luis Rocha, is trying to stop another ancient Djinn named Pearl from destroying humanity (what else!).

Unknown shares the same fast pacing with the Weather Warden series, with our heroine dashing from problem to disaster. Many people are caught up in the crossfire and she leaves a trail of dead bodies, most of which aren't her fault. The book hints at a romance, but this isn't particularly developed. While an enjoyable read, the action takes over too much, and I didn't really connect with any of the characters. Cassiel is clearly developing, but I wasn't entirely sure how it would play out. Pearl is also a bit too nebulous an enemy; not knowing the extent of her powers makes it hard to gauge the real level of jeopardy for Cass and humanity.

Although I enjoyed Unknown, I was a bit disappointed by the ending, which leaves most of the story hanging. I will probably want to read the next in the series, but this entry leaves a bit too much unfinished for full enjoyment.