"The Haunting of Villa Diodati" was written by Maxine Alderton. Chris Chibnall called Alderton "an absolute Mary Shelley and Byron… not a buff, she's an expert in that". Much of the setup of the episode is true to known fact for Lord Bryon, Mary, and the others, including that the summer during their stay at the villa was unusually stormy due to the 1815 eruption of Mount Tambora that led to the "Year Without a Summer".