Holocaust

Basically, the human race has survived one disaster after another, the latest being the destruction of the sun. To avert the total freeze, the few million that were left, fled through the solar system until they found Firan. Just as they got settled (about one hundred years later), blips appeared on their sky-tracker systems and they were under attack. Now, come on! You don't seriously expect anyone to have built more than one defense ship, do you? Thought not! And guess who they've got to fly it?