Crucible of Gold, by Naomi Novik. Unabridged audio.
This is one of my favorite ongoing series. Naomi Novik presents a plausible narrative of life during the Napoleonic Wars. Except that the world contains dragons. These are not mythical beasts, not magical beasts, simply very large (and reasonably intelligent) animals. It is a great premise, and more importantly, Novik has spun some great novels out of it.
At the start of this one, Laurence finds his rank restored, although he does not believe himself worthy. But Napoleon's arms have reached Brazil, and the country (and her dragons) appear poised to ally with the French, via the powerful African Tswana empire. The British government sees Laurance and Temeraire as their best hope of negotiating peace in South America. But the trip from Australia to Brazil is fraught with peril, with death and despair rampant.
Napoleon makes an appearance in the novel, arriving in Rio with a retinue of dragons and gifts. Having left Josephine, he is available as a potential spouse for the queen of the Incas. This is the last thing that Laurence needs if he is to accomplish his mission. The sense of dread, of the long odds against success in this mission, add a great sense of drama to the book.
There is a bit of repetition here, as Novik may be running out of interesting places to send Laurance and Temeraire. But the character aspects are strong as always, and all the characters (both human and dragon) have had interesting arcs over the sweep of the series. The discussion of marriage in this book gave the characters something new to discuss, and there are surprising revelations throughout.