Parts: 4
Writer: Eric Saward
Airdates: 15 February - 23 February 1982
Production Code: 5X

Doctor: fifth
Companions: Adric, Nyssa, Tegan

Creature Feature: Terileptils

Story: In the night skies over seventeenth-century England, a bright light resembling a comet flares into existence before bursting apart in a shower of colorful sparks. Having spied the lights, a young woman named Elizabeth excitedly runs to inform her father, but by the time she gets to him, they have vanished. But soon their home is breached by an alien presence which kills one of the servants. Elizabeth's brother wounds it, but his success is short-lived as a tall, gleaming figure breaks down the door to the dining room where they have barricaded themselves...

The next morning, the TARDIS materializes in the forest some distance away from the house. Tegan is huffy to learn that they have not landed at Heathrow as requested, but have missed it by three hundred years. Still, the TARDIS crew decide to take a look around, but they find themselves in a land paranoid from threat of the plague and extremely wary of strangers. Fortunately, they make the acquaintance of a most friendly actor, Richard Mace, who takes them back to the barn where he has made his temporary home. There, the Doctor and Nyssa spy various discarded alien artefacts, and when they learn of the previous night's comet, they persuade Mace to take them to the barn's owner.

But the house is mysteriously deserted, aside from signs of a battle waged with anachronistic weapons. When the Doctor discovers functioning alien technology within the house, he realizes that the aliens have made their base there. These aliens, Terileptils, soon capture Tegan and Adric, while the villagers, under their control, apprehend the Doctor. As Nyssa labors to construct a machine that will put the Terileptils' menacing android out of action, the Doctor and Mace must figure out how to put a stop to the aliens' plans...or the horror of the Black Death will be magnified a thousandfold and all life on Earth extinguished.