It is the destruction of Earth. A group of men manage to put together a spaceship to save them from imminent destruction. They travel light years to find a new planet to live on, and when they do, they find something they don't expect to. They end up on Equestria and must find a way to live in peace alongside their new colorful equine neighbors.
It starts out mostly focused on the humans, but I promise it gets to more ponies at the end. Another thing, I update the google docs version first so use that if you want to read more. It is unedited though.