Hired Gun and Serenity from "Fallout Equestria: Heroes" take a train ride as part of a job and cross paths Citquine and Celly from "Fallout Equestria: Wings" in this fun and completely non-canon stand alone adventure.
This story takes takes place in an alternate time line branching off some point after Chapter 11 of Heroes, so reading to that point would be helpful for understanding who the characters are. This story also takes place some time after the end of Wings, but knowledge of that series isn't too required.