Sarah Jane, Luke Smith, and Clyde investigate claims of sightings of a ghostly nun at Lavender Lawns Rest Home.

The sisters intend to use the talisman to connect Earth with the world of the Gorgons 100 million light-years away, an incorporeal parasitic race that inspired the Greek myth of the ugly woman with snakes for hairs, and take over the bodies of humanity.

The nuns take the talisman by force, and the Gorgon turns Maria's dad Alan to stone as he enters Sarah Jane's house, though it will take 90 minutes until the effect is permanent.

Chatting with Bea, Maria discovers that the talisman can revert those turned to stone to flesh and blood.

Bea gives Maria a mirror, which she uses at the abbey to revert the transfer and turn the Gorgon and its host body to stone, freeing the nuns of mind control.