The third book in the original Skulduggery Pleasant series.
If you've read the previous Skulduggery books then you know what the Faceless Ones are - and if you know what the Faceless Ones are, then you can probably take a wild guess that things in this book are going to get AWFULLY sticky for our skeletal hero and his young sidekick. If you haven't read the previous Skulduggery books then what are you doing reading this? Go and read them right now, so that you know what all that stuff in the previous paragraph was about. Done? Good.
So now you're on tenterhooks too, desperately awaiting the answers to all your questions, and instead you're going to have to wait to read the book. Sorry about that.