This the 11th book of the series Dragonriders of Pern. It follows immediately from the final scene of Renegades of Pern, in which the Admin building from Pern's first generation of colonists is discovered, along with an advanced computer called AIVAS (Artificial Intelligence Voice Address System), at the Landing site that is being excavated.

AIVAS has remained undisturbed since the events of Dragonsdawn some 2500 years earlier and, in addition to holding a huge volume of stored information long since lost to the Pernese society, claims to be able to eliminate the threat of Thread forever.

The Weyrs, led by Lessa and F'lar, enthusiastically embrace this possibility, and with the support of the Holds (led in particular by Jaxom) and the Crafthalls (championed by Masterharper Robinton) proceed to implement the ambitious plan under the careful guidance of AIVAS.

Aivas itself had been programmed to speak with a masculine-analogue, inquisitive, somewhat humorous personality, which gave the impression of a light-hearted counsellor to the Pernese, who have no real concept of what artificial intelligence entails.