This is the sixth book in the Temeraire series. I've read all the previous books, although not recently. If you haven't read any of them, you really shouldn't start here. Novik drops the reader into the story without trying to catch us up. I don't have any problem with that, myself, but it would be difficult to figure out what's going on if you haven't read any of the earlier books. You wouldn't even be able to figure out Temeraire is a dragon right away.
The series is set during the Napoleonic wars, but this world has dragons. In the first book, sea captain Will Laurence captures a French ship carrying an unusual dragon egg; when the egg hatches, the dragonet inside chooses Laurence as his companion, and Laurence has to leave the Navy and join the Aerial Corps instead. It's a great book.
The other books are good too, but oddly enough, nothing much really happens in them. The characters typically travel a great deal in some foreign land, maybe participate in a few battles, Temeraire discusses philosophy with Laurence and with the dragons and people they meet along the way, and at the end the war advances in a new direction. That's not to say the books are boring at all; I can't stop reading them once I start, and I'm really looking forward to the next book (there are nine planned). But they're slow-moving.
This one takes place in Australia, which is still a penal colony with only one city, Sydney. Laurence and Temeraire have been transported for treason, but they're soon given a useful task: search for a pass through the mountains. But things go awry, and soon they're chasing across the continent after a group of thieves and/or smugglers.
Temeraire is an appealing character, and Laurence's relationship with him is always charming to see. It's really the characters, and the good writing, that keep me interested in this series. (Although I must say, I don't reread any except the first book, and then I skim all the battles, so I refuse to buy these books in hardcover and have to wait for the paperback to come out, a year or so after.)