Series 12 of Doctor Who brought the titular character to Switzerland to meet Mary Shelley, the author of the horror icon Frankenstein at Villa Diodati on the night she created him. However, what many fans may not realize is that this isn't the first time the Doctor and Mary Shelley have met. When the Doctor was in her 8th incarnation, Mary Shelley was one of the Doctor's companions and traveled with him in the TARDIS for multiple adventures.
Relatively unknown to many modern fans, Paul McGann's Eighth Doctor did not appear in either the classic or current series of Doctor Who but instead starred in a one-off television movie in 1996. The movie was a back-door pilot for a revived show, but when that failed to materialize, the BBC gave a company named Big Finish the license to create a series of full-cast audio dramas starring the Eighth Doctor.
In these stories, McGann's Doctor frequently mentioned knowing the famous author, and after spending eight years hinting at it, Mary Shelley finally made her Doctor Who debut in 2009's Mary's Story. Strangely enough, this story is also set at Villa Diodati on the night of Frankenstein's creation, but in this version, it's the Doctor who haunts the villa until Mary manages to help cure him. After the adventure is over, the Doctor offers to let her travel with him, and she agrees.
Although it's implied she traveled with him for a long while, Mary Shelley is only the Doctor's primary companion for a trilogy of stories from 2011. The first, The Silver Turk, features Shelley's first trip in the TARDIS as the Doctor takes her to Vienna in 1873 where they encounter two damaged Cybermen. Mary initially took pity on the creatures and even helped repair them using "Galvanic lightning," but after nearly killing her while attempting to signal their home planet for reinforcements, Shelley destroyed their signal device soundly and defeated them.
The second story, The Witch from the Well, lands the TARDIS team in England during the early 2000s. Here they discover a nightmare buried in the well of an ancient house, but when they travel back in time to discover its source, they soon become trapped in the midst of a witch hunt in the 1650s. They soon discover that the future terror and the past "witch" are one and the same in the form of an alien being called a "Varaxil." Working together across two different time periods, the Doctor manages to trap the creature in the well in the past while Mary defeats it in the future.
In Army of Death, Shelley's third and final story as the Doctor's traveling companion, the famous author traveled to the alien planet Draxine and helped the Doctor defeat an alien being named Karnex and his undead armies of the planet's former citizens. After this adventure's end, Mary Shelley finally chooses to leave the TARDIS in order to escape the Doctor's only constant companion: death. The Time Lord returns Shelley to her proper place in time and space, and they part ways as Shelley begins to write a new book.
Mary Shelley made her return to the franchise earlier this year in "The Haunting of Villa Diodati." The story shows Jodie Whittaker's Thirteenth Doctor take her three companions Yaz, Graham and Ryan to see Shelley on the night she creates the idea of Frankenstein. Their visit is intermittently interrupted by a series of haunted happenings that ultimately result in a Lone Cyberman attacking the house.
"The Haunting of Villa Diodati" and Mary's Story show paradoxical and contradictory versions of the same event on the same night, and though it might be possible to reconcile these differences, this is nothing new for the franchise. Doctor Who has always had a loose sense of continuity that is more than comfortable embracing the existence of such paradoxes, and the idea that the Doctor's future meets Mary's past in "Haunting" before the Doctor's past meets Shelley's future in Mary's Story is exactly the kind of time travel shenanigans that its fans often enjoy.