Superhuman mission for Golan Trevize: choose the best future for humanity. A future that will not repeat the errors of the Galactic Empire, between the materialism of the First Foundation and the mentalism of the Second. A future whose model is Gaia, the thinking planet, and whose name is Galaxia. Trevize has chosen, but he would like to know why. And the answer to his questions lies on Earth. But where to find it, this planet of origins, mysteriously disappeared from all galactic archives?