From the introduction:
You were in the sky when it started, in ships among the stars. The threat came suddenly, and the response was clear - leave, now. You left without saying goodbye, without looking back. Now, you and your fellow pilots returned to circle the planet you once called home, and something went wrong. And now you’re stranded. The threat remains, and the few groups of survivors who remain are either suspicious of your arrival or angry at your departure. So that just leaves you, your crew, and the ruined wasteland of somewhere that used to be home.