Across the Wall: A Tale of the Abhorsen and Other Stories by Garth Nix
This is a collection of short stories by Garth Nix with the largest being a short continuation of the Abhorsen trilogy. The main character is Nick Sayre, who was the unwitting puppet of the destroyer in Abhorsen. In this story Nick is trying to return to the Old Kingdom, but finds difficulty when he is confronted by an evil creature of free magic. This story was interesting and if you liked the Abhorsen books, than you'll like this as well.