Despite how quickly I devoured the three first Sally Lockhart books, I took my time getting around the the fourth because, well, it's not about Sally. She only appears in the book very briefly. I shouldn't have waited so long.
The Tin Princess is a fast-paced, engrossing Victorian pulp, told with the keen eye for imperial politics and business that Pullman has brought to all the books in this series. Although I didn't remember Adelaide very well from the first time I met her, I quickly grew very attached to her, and Jim, and Becky. (It doesn't hurt that Jim Taylor was played in the BBC movie by Matt Smith, the newest Doctor.)
The book starts with Becky, a young expatriate living in London, with her mother, with a facility for languages and a thirst for adventure - in theory, anyway. Becky is engaged to teach German to Prince Rudolf of Razkavia's new bride, the aforementioned Adelaide, still half the street urchin we knew her as, but with the wit and ability to appear as gracious and anyone. A few assassination attempts later, and Adelaide, Becky and Jim are off to Razkavia, where they struggle to keep the country free from the imperial designs of Austria and Germany.
All four of these books are great reads for young adults, but also bring a keen eye to the troubles of Victorian England (how many young adult books do you know that go into great detail about the complicity of the British Empire in the opium trade, for instance? Or the legal position of unwed mothers in Victorian England? Or (in this one), the blind eye England turns to everything that is going on.)