The Doctor (Ncuti Gatwa) and Ruby (Millie Gibson) arrive at the top of a cliff in Wales. The Doctor accidentally steps on a fairy circle with two scrolls inside it. Ruby finds a message on one of the scrolls which reads, “Miss you” and “Rest in peace, Mad Jack.” Suddenly the Doctor vanishes. A mysterious woman (Hilary Hobson) appears 73 yards away from Ruby and maintains that distance no matter where she goes. Everyone who talks to the woman runs away in terror and shows hostility to Ruby.
Ruby returns home and asks Carla (Michel Greenidge) for help. Carla also flees from the woman and disowns Ruby. A year later, Ruby has a meeting with Kate Lethbridge-Stewart (Jemma Redgrave) of UNIT, who tells her no-one has seen the Doctor and comments on the increase in supernatural activity recently detected by UNIT. She wonders if the perception filter of the TARDIS may be responsible in some way. Some UNIT soldiers try to capture the strange woman, but when she speaks to them, Kate cancels the operation and abandons Ruby, who spends the next 20 years alone.
On a date, Ruby sees an advertisement for Roger ap Gwilliam (Aneurin Bernard) running for Prime Minister. She recalls the Doctor saying that Gwilliam would bring Britain to the brink of war if elected. His nickname is Mad Jack, and she thinks that connects him to the fairy circle. She joins his campaign to stop him, but he wins the election and then plans to take Britain out of NATO and buy the Pakistani nuclear arsenal. Ruby stands 73 yards from Gwilliam and he encounters the woman. He flees in terror and resigns.
But the woman does not leave, and Ruby spends another 40 years alone. Lying in a hospital bed as an old woman, she is approached by the woman and Ruby’s heart monitor stops. Then Ruby reappears in the past just as the Doctor steps into the circle. She watches from the strange woman’s position and warns her younger self, who prevents the Doctor from stepping into the fairy circle.
The episode was written by Russell T. Davies and directed by Dylan Holomes Williams. It received rave reviews from critics, particularly Millie Gibson’s performance. It was nominated for a Hugo Award. It garnered 100% on Rotten Tomatoes and was praised as a sci-fi horror classic. Some reviewers groused about the unanswered questions in the story, but most found them intriguing and effective.
Davies called it a Welsh Folk Horror, and it was genially creepy. He was immensely proud of it. The idea was that Ruby had to do a good deed and live a punitive life because the Doctor violated a fairy circle. The pub scenes were filmed at the White Cross Inn, which had appeared in the Torchwood spin-off series. An audio book was read by Susan Twist.