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.

Maria's dad Alan (Joseph Millson) has been turned to stone. The alien talisman is now in the possession of the Gorgon and her evil nuns, and they are preparing to open the portal to their world. Can Sarah Jane (Elisabeth Sladen) and her young friends free Alan from his stony state, prevent the nuns from unleashing more deadly aliens on the Earth, and avoid the Gorgon's petrifying gaze?