The White Dragon: Dragonriders of Pern, Book 3

Never had there been as close a bonding as the one that existed between the daring and adventurous young Lord Jaxom and his extraordinary white dragon, Ruth. Pure white and incredibly agile, Ruth was a dragon of many talents, though almost everyone on Pern thought he was a runt that would never amount to anything.

But Jaxom knew better, knew he could teach his dragon to fly and to destroy the deadly silver Threads that fell from the sky. Disobeying all rules, Jaxom and Ruth trained in secret. Their illicit flights seemed but a minor disobedience - until they found themselves in the path of danger and in a position to prevent the biggest disaster of all.