The Naming of the Beasts (Felix Castor #5) (2009) by Mike Carey (a.k.a. M.R. Carey): Argh! Mike Carey hasn't written a Felix Castor novel since this one. Come back, Mike! Freelance exorcist Felix Castor finally gets his showdown with the demon Asmodeus, who's in possession of the body of Castor's best friend. Asmodeus is out and about in London, up to something that will free him from his unwanted mortal vessel without sending him screaming back to Hell. Meanwhile, the supernatural world seems to be shifting, changing the rules that have only been in place for the ten years since ghosts, demons, and other beings were inexplicably unleashed on Earth.
Castor is a fun hybrid of hard-boiled detective and snarky, ironic commentator. Carey's put a lot of thought into Castor's world, in which scientists and occultists alike try to master the spirit world before it masters them. If there's a flaw here, it's that it's hard to care about Felix's best friend Rafi. He willingly participated in the ritual that stuck Asmodeus in him.
Moreover, we've never seen him unpossessed in the series: we're told over and over again what a charming rogue he is, but we never really have that shown to us. It makes the stakes somewhat light: like some of Castor's occult colleagues, I find it hard to justify worrying so much about keeping Rafi alive when the demon riding his body is racking up such a death toll.
But other than that and a last couple of pages that reminds me of all those 1960's and 1970's American TV dramas that ended with everyone standing around laughing despite the catastrophes that came earlier in the episode, The Naming of the Beasts is a fun and often wildly imaginative ride. More Castor please! Recommended.