There was a portal that appeared in the sky that sucked up every resident of Ponyville into an almost uninhabitable post-apocalyptic planet, Twilight takes it upon herself to find and bring everypony back home to the safety of Equestria.
Twilight knows she can't do it alone so she enlists the help of an old mercenary to assist her, she doesn't know what this new world can hit her with so hopefully this person is nice enough to not instantly shoot her.