Isobel (Izzy) was an indentured servant since the age of 2. She gains her freedom on her 16th birthday. She then opts for a Bargain (this is for life) to serve the devil (that's what he is called) as his Left Hand.
Gabriel is an experienced rider and his expertise is enlisted to help Izzy learn the ropes. The world was confusing at first- this is a re-imagining of the old west. The US exists east of the Mississippi River and everything to the west is either under Spanish protection (CA, AZ, NM, parts of TX), unclaimed (WA, parts of OR, ID), or part of the devil's territory. The US and the Spanish are trying to expand into the Devil's territory.
This had an interesting start but then got very slow. There was Something going on, but they were consistently arriving after the fact. Lots of traveling, but not actually doing anything useful. The big thing was figuring out Izzy's new role and talents. And at the end, it was still unclear (at least to me).
This is a trilogy with a few short stories too. While I liked Izzy and Gabriel, this was too slow for me and I don't care to continue.
For Romance-opoly Journey's End sun track.