The Witch of Clatteringshaws (The Wolves Chronicles, #11)

The Witch of Clatteringshaws lives in Scotland in a disused Ladies Convenience - not at all convenient, the plumbing having long been smashed. In London, Simon Battersea, unhappily settled on the throne of England, is forced to live in St James's Palace with his good friend, Dido Twite. Never has Joan Aiken's wild imagination been more in evidence as Dido, travelling north to investigate a false claimant to the throne, is confronted by abandoned children, monsters and murderers, while Simon has to defend his country against invading Wends.

Their instinct to go north is a good one for it is the witch, Malise, who provides the key to everyone's troubles in a wonderfully swift and extravagant climax. A tremendous read and a truly satisfying ending to the Dido and Simon saga.