Vacant Possession

Eighty years ago, hostile aliens scoured most of humanity from the surface of the Earth with a monstrous weapon that left the planet uninhabitable for humans. Friendly alien rescuers helped the survivors build a refuge on the moon and people from all over the world united in this new home they called Tranquillity City. Only a handful of the original survivors are still alive. Now the city is populated by their children, grandchildren and great grandchildren.
Most of those don't even think about their ancestral home planet. But when the oldest human alive learns that the same aliens who rescued the last human survivors are petitioning the galactic court to allow them to take ownership of the uninhabited Earth, she knows what has to be done to reclaim their lost home planet. It's time for humans to invade the Earth.