In this book, past events are “entangled” under the guidance of an artificial mind created by the ancestors—Aivvas. He made the Scarlet Star move along another orbit so that it would stop bringing fatal threads from space to Pern. And thus they saved Pern from this terrible calamity.
Also, thanks to Aivvas, forgotten technologies of the ancestors are revived on Pern, provoking resistance from the opponents of the new.