Skulduggery Pleasant 6. Death Bringer

Meet Skulduggery Pleasant: detective, sorcerer, warrior.
Oh yes. And dead.
The Necromancers no longer need Valkyrie to be their Death Bringer, and that's a Good Thing.
There's just one catch. There's a reason the Necromancers don't need her any more - because they've found their Death Bringer already, the person who will dissolve the doors between life and death.
And that's a very, very Bad Thing...