"The Haunting of Villa Diodati" is the eighth episode of the twelfth series of the British science fiction television programme Doctor Who, first broadcast on BBC One on 16 February 2020. It was written by Maxine Alderton, and directed by Emma Sullivan. The episode stars Jodie Whittaker as the Thirteenth Doctor, alongside Bradley Walsh, Tosin Cole and Mandip Gill as her companions, Graham O'Brien, Ryan Sinclair and Yasmin Khan, respectively. The episode is about the historical origins of the 1818 novel Frankenstein; or, The Modern Prometheus by Mary Shelley, portrayed by Lili Miller, and takes place at the Villa Diodati in 1816 where she was inspired to write the work. The episode also featured the return of the Cybermen in their first television appearance since the tenth series finale "The Doctor Falls" (2017). The episode was watched by 5.07 million viewers, and received positive reviews from critics.

The Doctor takes Graham, Ryan and Yaz to Lake Geneva in 1816 to witness Mary Shelley gain the inspiration to write Frankenstein, though she warns them about revealing this to her. Meanwhile, Mary, her infant William, along with John Polidori, Claire Clairmont and Lord Byron are staying at the Villa Diodati. Mary's fiancé Percy Bysshe Shelley, is inexplicably missing. Because of the inclement weather, Byron suggests each write a ghost story to scare the others. Later, the Doctor and her companions arrive, only to discover that the expected ghost story sharing has been abandoned, and that Percy is not there, although he should have been.

Strange events occur in the villa, such as the repeated rearrangement of its layout, objects moving of their own accord, and skeletal hands crawling around the halls. Byron suggests it is a ghost that haunts the villa but the Doctor suspects something else is occurring; the events are part of a security system designed to hide something. The group sees an apparition which the Doctor recognises as a being moving through time; the apparition resolves into a half-converted Cyberman.

Graham, Ryan and Yaz remind the Doctor of Jack Harkness's warning of the "lone Cyberman" and giving it what 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 then his power had 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. Meanwhile, the Doctor discovers Percy's room, the walls of which are covered in strange gibberish in his handwriting.

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. The Doctor loses her temper with her companions and brings Percy to Ashad and to stop Ashad from killing him, tricks the Cyberium into leaving Percy's body and entering hers. Ashad threatens to destroy the planet, forcing the Doctor to turn the Cyberium 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.