There exist two worlds - one, where humankind is on the brink of extinction at the hooves of a Celestia who doesn't believe in ponification being optional; and another world, where ponies aren't mindless slaves, and Equestria's never heard of humans before.

A portal is made, and an exchange happens; a bomb-suited human from a dystopian, war-torn Earth goes to a better place and tries to deal with the fact that not everything wants him to have hooves, while he tries to find a way back to the Earth he's more comfortable with. Meanwhile, two mares from a peaceful Equestria are pulled into a world where ponies are treated as the enemy, and try to negotiate a cease-fire on behalf of the humans, as they struggle to end the bloodshed.

It sounds like the impossible, but humanity doesn't have a choice.