The Creature in the Case by Garth Nix
Exclusive new adventure set in the Old Kingdom, set approximately six months after the events in ABHORSEN. Nicholas Sayre is still recuperating from the injuries he received at the hands of the Destroyer. But after several idle months in Ancelstierre, he is desperate to return to the Old Kingdom, so when the opportunity arrives to actually DO something, he accepts like shot. As a favour to his Uncle Edward, the Chief Minister of Ancelstierre, he travels to spend the weekend in a remote country house, the home of a family which would make a good political alliance. That seems easy enough, till he discovers that the house holds many secrets, and the worst of them is a relic of the Old Kingdom, too far from the Wall for any spark of its magical life to reignite. Unless someone finds a way to unleash its power!