Sarah Jane (Elisabeth Sladen) and her young friends investigate reports of a ghostly nun which is haunting the local old folks' residential home. And when one of the elderly residents entrusts Luke (Tommy Knight) with a mysterious alien talisman, it becomes clear there is even more to the story than meets the eye. The gang delves deeper, and discovers that the nun is part of a secret order sworn to protect a terrifying alien creature who can turn her victims to stone with a single look.