All the Weyrs of Pern: Dragonriders of Pern, Book 11

But the greatest dream of the dragonriders was to find a way to eradicate Thread completely, so that never again would their beloved Pern be threatened with destruction.

Now, for the first time, it looks as if that dream can come true. For when the people of Pern, led by Masterharper Robinton and F'lar and Lessa, Weyr-leader and Weyrwoman of Benden Weyr, excavate the ancient remains of the planet's original settlement, they uncover the colonists' voice-activated artificial intelligence system - which still functions. And the computer has incredible news for them: There is a chance - a good chance - that they can, at long last, annihilate Thread once and for all.