Gunslinger Lizbeth Rose lives in what used to be the United States, but after the assassination of FDR in the 1930s Texas and Oklahoma have become a small land of their own known as Texoma. Other parts of the US have been ceded back to Britain (the northeast), Canada (the upper midwest), and the far west the last Tsar to escape Russia. And the rest of the south (not Texas and Oklahoma) is known as Dixie and has reverted to a post-Civil War, reconstruction society in which race relations are very, very bad. As you can guess, along with geographic boundaries, much of the rest of 20th century infrastructure has broken down and Lizbeth makes a living as a hired gun who takes on jobs for those who need protection. Oh and there are Russian magicians!
This is the second book in the series and Lizbeth has been hired onto a new crew for a job that seems to be relatively straightforward. She and her crew are traveling by train from Texoma into Dixie where they're to deliver the crate they've been transporting (and guarding). Just as they're nearing their destination their train is attacked and most of the crew are either injured or dead and Lizbeth is left to fend for the cargo and herself in a country she doesn't know and that isn't particularly hospitable to lone women. Lizbeth is up for anything, but she's certainly relieved when an old acquaintance appears and offers to team up so that she can finish her assignment.
Charlaine Harris is just so good at creating her alternate versions of our world and history and then peopling them with characters who are well-developed, one and all. If you haven't yet read book one of this new series, start with An Easy Death first.