It's a ghost story on this week's Doctor Who! This episode once again sees the Doctor and Clara off on another adventure, this time to a creepy old house.
In 1974, a professor named Alec Palmer and his assistant are trying to find evidence of a ghost known as the Witch of the Well. The assistant, Emma, apparently has psychic powers that can summon ghosts. Instead of grabbing a ghost however, the Doctor and Clara arrive.
The Doctor becomes interested in the investigation when Clara notices that the ghost is in the same position in each of Palmer's photographs. the two come upon a spot in the house that is quite a bit colder. Suddenly, the entire house becomes ice cold and Clara feels like something grabbed her hand. Using her psychic powers, Emma is able to sense someone asking for help through a mysterious black portal, before it disappears and the house returns to normal.
The Doctor decides to study this cold spot at different points throughout the planet's history, finding that it's some kind of door to another dimension. Whoever was asking for help is trapped on the other side. He helps Emma to develop her abilities in order to open the gateway. He tethers himself to one side, and crosses over through the portal to rescue whoever is on the other side.
In the "pocket dimension," the Doctor meets Hila Tukurian, a fellow time traveler who had become trapped. She warns that something else is in there with them. As they try to escape, whatever that something is begins to give chase, and only Hila makes it out before an exhausted Emma is unable hold the portal open any longer.
Luckily, some quick thinking on Clara's part is able to send the TARDIS in to save the Doctor. As the two prepare to leave, the Doctor reveals that he stopped at this point in time to see if Emma could sense anything strange about Clara. Unfortunately, she doesn't have any answers.
Before departing, the Doctor learns that Hila is actually a future descendant of both Emma and Alec, which furthermore makes him realize that the creature in the pocket dimension was just trying to escape as well. He asks Emma to open the portal one last time to rescue it.
The Doctor will return on "Journey to the Centre of the TARDIS," which promises to show more of the Doctor's traveling device than ever before. It airs on April 27.