Ptolemy's Gate (Bartimaeus Trilogy, Bk. 3)

Three years after the events of The Golem's Eye, the young magician Nathaniel is an established member of the British Government. But he faces unprecedented problems: foreign wars are going badly and Britain's enemies are mounting attacks close to London. Increasingly distracted, he is treating Bartimaeus worse than ever: the long-suffering djinni is growing weak from too much time in this world, and his patience is at an end. Meanwhile, undercover in London, Kitty has been stealthily completing her research into magic and Bartimaeus' past. She hopes to break the endless cycle of conflict between djinn and humans - but will she be able to get anyone to listen? Before any of these problems can be resolved, disaster strikes London from an unexpected source and the destinies of Bartimaeus, Nathaniel, and Kitty are thrown together once more.