One stormy night in November 1974, Major Alec Palmer (Dougray Scott) and his assistant Emma Grayling (Jessica Raine) try to make contact with a spectre, known as the Witch of the Well, which has been haunting Caliburn House for over 400 years, when some other ‘ghost busters’ arrive: the Doctor and Clara.
Haunted by the guilt of the many deaths he saw during the war, Major Palmer has become obsessed with finding proof about the afterlife. Helping Palmer is Emma Grayling (Call the Midwife actress Jessica Raine), an empathic psychic who is actually in love with Palmer, but she is as frightened to make the first move as he is.
While studying photographs of the spectre, the Doctor notes that the spirit is always in the same position and that something is chasing her. The spirit then makes itself known, begging Emma and Alec to help her. Borrowing Palmer’s camera and boarding the Tardis, the Doctor and Clara travel Earth’s entire six-billion-year life cycle to take a snapshot once every million years. But the Doctor’s lack of empathy over the eventual death of the Earth and its inhabitants worries Clara, who has been warned by Emma not to trust the Doctor.
Back at Caliburn House, the Doctor’s photographs reveal that the ghost is in fact a pioneering time traveller, Hila Tacorian (Kemi-Bo Jacobs), who has become trapped in a pocket universe. To save Hila, the Doctor creates a wormhole using Emma’s psychic power and a blue crystal from Metebelis III, and heads into the echo universe. Locating Hila, the Doctor leads her to an exit, but the wormhole closes before he can cross over. Clara then uses the Tardis to retrieve the Doctor.
Back at the mansion, the Doctor reveals that the psychic link between Hila, Emma and Alec was due to the fact they were blood relatives – meaning that Emma and Alec belong to each other. The Doctor then realises that the creature was also trying to make contact – with its lost mate – making his latest adventure a love story rather than a ghost story. The episode ends with the Doctor and Clara setting off to reunite the creatures, but not before the Doctor takes Emma aside and asks her about Clara. But she reveals nothing…