In November of 1974, Professor Alec Palmer (Dougray Scott) and his assistant Emma Grayling (Jessica Raine) collect photographic evidence of a ghost at Caliburn House. Professor Palmer uses Emma’s psychic powers to summon the spectre. The Doctor (Matt Smith) is interested, but it’s Clara (Jenna-Louise Coleman) who points out that the ghost is in the same position in each picture.

The Doctor and Clara go back in the TARDIS to photograph that location at various points in Earth’s history. The Caliburn Ghost appears to be a pioneer time-traveller named Hila Tacorian (Kemi-Bo Jacobs), trapped in a pocket universe where time passes more slowly. The Doctor invents a device to allow Emma’s psychic abilities to open a gateway. The intention is for the Doctor to anchor in this world and cross in a harness to take Hila back. Are we thinking of Spielberg’s Poltergeist?

He finds Hila, but they are chased by a creature in the forest. Hila is saved, but the Doctor is trapped. Clara pleads with the TARDIS to help him, and it finally lets her in. The Doctor jumps and hangs on to the TARDIS before the creature can grab him, and he returns. The next morning, the Doctor asks Emma if she senses anything unusual about Clara, but she has noticed nothing. I would say it’s pretty unusual for companions to converse with the TARDIS.

The Doctor thinks that Hila is a direct descendant of Emma and Palmer, which helped Emma open the gateway. He thinks there is another creature in the house and the creature that chased them is its mate. They use Emma and the TARDIS to rescue the other creature from the pocket universe.

Tyntesfield House, a lovely Gothic monstrosity in North Somerset, played the Caliburn House. The writer Neil Cross was in New Zealand the whole time during the writing, though he flew in to watch the filming. He wanted the Doctor to find Bernard Quatermass in the story, but that was impossible for copyright reasons. There were only six characters in the whole story. It was the first episode Jenna-Louise Coleman filmed as Clara, chosen on the strength of a five-minute audition for Asylum of the Daleks.

The Doctor uses a blue crystal from Metebelis III, as in Jon Pertwee’s episodes The Green Death and Planet of the Spiders. He wears the orange spacesuit David Tennant did in The Impossible Planet/The Satan Pit, and other episodes. Neil Cross’s children were monster consultants to make sure they were scary enough. The episode was largely inspired by The Haunting of Hill House (1959) by Shirley Jackson.