Lili Miller – Mary Wollstonecraft Godwin
Jacob Collins-Levy – Lord Byron
Nadia Parkes – Claire Clairmont
Maxim Baldry – Dr John Polidori
Patrick O'Kane – Ashad
Lewis Rainer – Percy Bysshe Shelley
Stefan Bednarczyk – Fletcher
Sarah Perles – Elise
Directed by Emma Sullivan
Written by Maxine Alderton
Script editor: Fiona McAllister
Produced by Alex Mercer
Executive producer(s): Chris Chibnall, Matt Strevens
Incidental music composer: Segun Akinola
Length: 49 minutes
First broadcast 16 February 2020
The Doctor takes Graham, Ryan, and Yaz to Lake Geneva in 1816 to witness Mary Shelley gain the inspiration to write Frankenstein, though warns them about revealing this to her. The group meet Mary along with her husband-to-be Percy Bysshe Shelley and her infant William, along with John Polidori, and Claire Clairmont, and Lord Byron at the Villa Diodati. Because of the inclimate weather, Bryon suggests each write a ghost story to scare the others.
Percy soon goes missing, having left strange gibberish on the walls of his room, and strange events occur in the villa, such as the rearrangment of its layout. Byron suggests it is a ghost that haunts the villa but the Doctor suspects something else is occurring, the events part of a security system to prevent finding something. The group sees an apparition which the Doctor recognises as a being moving through time; the apparition resolves into a half-damaged Cyberman.
Graham, Ryan and Yaz remind the Doctor of Jack Harkness's warning of the "lone Cyberman" and giving it want it wants, but she angrily orders them not to follow her, and tells them to protect Mary and the others, before heading off to confront the Cyberman. The Cyberman, named Ashad, was sent back in time to look for the "Cyberium", a liquid metal with the collective knowledge of the Cybermen. Ashad had tracked it to the villa but since his power has been sapped. As the Doctor tries to lure Ashad away from the villa, he is struck by lightning, recharging his power core, and he prepares to attack the villa again.
The Doctor races to warn the others but instead finds Percy hiding in the cellar with a crazed look. She discovers he is possessed by the Cyberium, having found it a few days prior, and the Cyberium had created the supernatural events to prevent discovery. She brings Percy to Ashad, and to stop Ashad from killing him, tricks the Cyberium to leave Percy's body and enter hers. Ashad threatens to destroy the planet, forcing the Doctor to turn it back over to him, despite Harkness's warning.
The Doctor and her companions depart, making plans to follow Ashad to the future using coordinates from Percy's Cyberman-based writings. After they leave, Mary reveals to the others she was inspired by Ashad's appearance, "this modern Prometheus", and plans to write a story based on their experience.