Udilf and the people in his town are preparing for an attack. They spend their days making weapons and armour. They know that an attack by mysterious "creatures", who are invulnerable to their weapons, will come soon.
Udilf is called to the town gate by Mang. Outside the town are four travellers, and Udilf lets them in because they appear to be weaponless. Their leader introduces himself as the Doctor, and he tells Udilf that they have seen devastated villages on their way here. Udilf tells him of the mysterious attackers, and the Doctor persuades him to let himself and Adric look for the attackers to try to reason with them.
As the Doctor and Adric walk along, the Doctor informs Adric that the "creatures" are probably aliens that are stranded on Earth. The Doctor will offer to help them get off Earth. As the Doctor stops to examine animal droppings, Adric gets bored and wanders ahead. He is attacked by a scout, who, when learning what they are hunting, offers to take them to his leader, Czar U'thai.
In U'thai's camp, Adric and the Doctor learn that U'thai and his men are the "creatures". U'thai and his men are Asian, and Udilf's people have never seen an Asian before. Their invulnerability to arrows comes from their silk shirts, which allow them to remove any arrows effortlessly.
Meanwhile, in Udilf's village, Tegan and Nyssa help make weapons and armour. At the end of the day, they learn that the men will be fed before they are. When Mang tells the townspeople the story of his father's fights with the Romans, Tegan protests that at this point in history, the Romans are no more. Mang is offended that Tegan is questioning his story, and Nyssa drags Tegan away. The girls discuss the possibility that Earth's history has somehow been changed.
After entertaining U'thai with magic tricks, the Doctor and Adric sneak out and head back to Udilf's town. The Doctor and Nyssa want a peaceful solution, so the Doctor contrives tricks to scare away U'thai: blue-white flames and trenches for the horses to fall into. Tegan and Adric think they should fight, and Adric introduces the longbow to Udilf's people.
The attack comes unexpectedly at night, and the Doctor's tricks don't scare away U'thai. There is much fighting and many deaths. U'thai attempts to take Tegan, but the Doctor pins him to a tree with the longbow. He offers mercy to U'thai's men, and the townspeople are left to take stock of their losses.
On the way to the TARDIS, the travellers discuss the deaths and Adric's introduction of the longbow. The Doctor is less concerned with Adric's effect on history than he is with the deaths that will be caused by this early use of longbows.
- Tegan thinks her name is Welsh.
- According to the Doctor, King Ethelred died in 1016. As his name was mentioned, the Doctor uses this to estimate the date when they've arrived.
- All the stories in Short Trips: Past Tense take place some time in Earth's past. This story takes place in 11th century eastern Europe.
- The Doctor has recently regenerated. (TV: Logopolis)
- The Doctor learned how to shoot a bow and arrow from Robin Hood. (PROSE: The Thief of Sherwood)