Moreta, Weyrwoman of Fort Weyr, attends the first Gather of Alessan, The Lord Holder of Ruatha Hold. Disaster strikes most of Pern in the form of a Plague. Both come down with the illness but recover to assist the other sick and dying. Because the sickness strikes both runner beast and humans, Master Healer Campian realizes that the infectious agent can be caught again by either party from the other. Moreta and several other dragonriders are called into service to travel across Pern to head off another outbreak - if they fail the destruction of Pern is likely.