We learn that what has happened to Sue and Eadgils is not quite unique, as the world's oldest Immortal has seen something similar once before, and he tells the sad story.

Brian didn't know what he had gotten into when he responded to a Unicorn's summons. He didn't know the ropes of the job and had short of forever to learn it. He had become a Unicorn. But worst of all, the job description didn't mention the fact he would become a she...