For Christmas Eve is also hallowed to dark forces, powers older than mankind. Women disappear in the dark of night, and reappear no longer sane. When Nan, Sarah and the Watsons are called on to examine these victims, they discover that it was no ordinary horror of the streets that drove them mad. It will take the combined forces of Magic, Psychic Powers, and the world's greatest detective to stop the darkness before it can conquer all.