This is the first book in this series, although there are a couple of short stories that are prequels to this novel, and do a lot of the world-building. I haven't read them (yet), but Sharp does enough filling in of the backstory so that I had no trouble following the story.
This is a YA steampunk adventure which features plenty of action, a strong female protagonist, some suitably evil villains, a good support cast for our heroine, and a bit of romance. No dates are mentioned, but some of the exposition reveals that aliens came to Earth about a century ago, gave humans (or perhaps just the British) a star drive, and made Queen Victoria immortal. These are details that I assume are covered in the prequel short stories. This would set the story in the latter half of the 20th Century, although the time period is not relevant, as it is essentially Victorian era with space ships and ray guns.
The pace moves pretty rapidly and there are no real plot twists - at least none that came as much of a surprise. Overall, a quick and enjoyable read.