The Creature in the Case (Abhorsen 3.50)

It is six months since the cataclysmic events of Abhorsen, six months Nicholas Sayre has spent recovering in the Ancelstierre. But he is desperate to return to the Old Kingdom, and at last has the chance.

All he has to do is spend a weekend in a country house as a favour for his Uncle Edward, Chief Minister of Ancelstierre. 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....