The Empress of Mars by Kage Baker
My rating: 4 of 5 stars
This here is a great book. I'd picked it up on a whim, used, without knowing much about it other than it says it's one of Kage Baker's "The Company" series.
Amusingly, it's not obviously part of that series, and if you're worried about picking this book up and not knowing what's going on, don't worry - there's no obvious metaplot here, and although it's apparently part of the future history of her series, there's no reference to any other part of it.