They came to our world a hundred years ago. Before we knew it they overran the world, destroyed our infrastructure and now we live in habitats. That's the best we can call our living accommodations. They terraformed the world...
What remains of humanity whispers about a plan to evacuate some of us. They claim that scientists hid away in a bunker somewhere where they retro-fitted one of their spaceships.
We don't know if it's true, but as we watch them lead away groups of humans from the nearest habitats, we decide to chance our escape.