And then, it ended. The main Earth fleet was still two months out when the aliens on Earth all packed up and went back to Mercury -- one day they were on Earth playing cat-and-mouse with Earth defenders and raiding sheep herds, and the next they left.
Two days after the little ships arrived at Mercury, the big ship launched. It headed back towards the Altair HX fragment at about the same acceleration that it had been using to reach the Solar System. Whatever it had needed to do in the Solar System, it had done, and it was now headed back. It passed close to the returning Earth fleet, but didn't make contact.
The crisis was over, now we people of the Solar System had to decide what to do about it.