Dragonquest (Dragonriders of Pern Series)

Another Turn, and the deadly silver Threads began falling again. So the bold dragonriders took to the air once more and their magnificent flying dragons swirled and swooped, belching flames that destroyed the shimmering strands before they reach the ground. But F'lar knew he had to find a better way to protect his beloved Pern, and he had to find it before the rebellious Oldtimers could breed anymore dissent... before his brother F'nor would be foolhardy enough to launch another suicide mission... and before those dratted fire-lizards could stir up any more trouble!