In the final book of the Bartimaeus trilogy, tension is increasing in eighteenth-century London. More and more commoners are being born resistant to the spells of the high-ranking magician class, and the underground movement, the Resistance, is growing. Led by a girl named Kitty, it grows despite the magicians' best efforts to curb its strength. Nathaniel, a young magician whose success in the previous books has boosted him in the ranks of magicians, has started to treat his djinni Bartimaeus worse than ever. After spending too much time cooped up in an earthly form, Bartimaeus is becoming weaker than ever. The stories of Nathaniel and Kitty finally converge as djinni decide to voluntarily come into our world - and take their revenge.
Personally, I thought this book was a great ending to the series. It solidifies the mechanics of the djinni and the Other Place and explores the relationship between Nathaniel and Kitty, as well as the bond between the djinni Bartimaeus and his old master, Ptolemy, possibly the only person to not only appreciate the sacrifices made by the djinni, but to make a sacrifice of his own, one so great it affected him until his death, where he dismissed Bartimaeus before he could die as well. It's a good addition to the story because it explains why Bartimaeus acts the way he does to Nathaniel and Kitty.