Bartimaeus Trilogy, Book Three: Ptolemy's Gate

Three years have passed since the magician Nathaniel helped prevent a cataclysmic attack on London. Now an established member of the British government, he faces unprecedented problems - foreign wars are going badly, Britain's enemies are mounting attacks close to London, and rebellion is fermenting among the commoners. Increasingly imperious and distracted, Nathaniel is treating Bartimaeus worse than ever. The long-suffering djinni is growing weak and vulnerable from too much time in this world, and is nearing the end of his patience. Meanwhile, Nathaniel's longtime rival Kitty has been stealthily completing her research on magic, demons, and Bartimaeus's past. She has a daring plan that she hopes will break the endless cycle of conflict between djinn and humans. But will anyone listen to what she has to say?