Slobeslav Stojespal is running from the Nockrauler, but it attacks him. He is rescued just in time by the Doctor and Peri, who had hoped to arrive in Prague in 4240 but have found that it's 1689. They take Slobeslav home, and when he recovers, he explains to them that the night sky is different from what it used to be and that they have had no news from outside the city in several years. The Doctor realises that 17th century Prague has been taken out of its normal time and place.
The Doctor sends Peri to the TARDIS to retrieve his universal adaptor, but as she walks along the Vltava River, she notices that it is made of black "gloop". She returns to the Doctor and tells the Doctor that the city appears to be sinking into the gloop, but the Doctor tells her the city is coming out of the "ooze" and sends her back to the TARDIS. When she arrives, a soldier tries to arrest her. When she runs away, she falls into the river and is absorbed by the ooze.
After a while, the Doctor notices Peri hasn't returned and goes looking for her. When he arrives at the TARDIS, the soldier tries to arrest him but the Doctor elicits from him the fact that Peri fell into the river. The Doctor decides he needs to see the king.
His meeting with the king doesn't go well. He tries to explain that Prague has been brought out of time and space by an artificial intelligence that is replicating Prague after a time-space rift attracted its attention. When the Doctor tells Edmund the First that he needs his gold medallion to destroy the Nockrauler, Edmund thinks he's crazy and tries to have him arrested.
At that moment, however, the Nockrauler appears. The Doctor notes that Peri is contained within the monster, and she is holding the universal adaptor. The Doctor talks to her, and eventually she is able to force the Nockrauler to give the Doctor his device. He uses it and the medallion to destroy the Nockrauler.
With Prague back to normal, the Doctor tells Slobeslav that he has destroyed the artificial intelligence and the people can make Prague into what they want.
- The medallion was made from gold that Richthausen made out of mercury for Ferdinand III.
- The Doctor and Peri think the river smells like black pudding.
- The Doctor mentions the Thirty Years' War.
to be added
- The Doctor and Peri refer to their encounters with the Daleks (TV: Revelation of the Daleks), the Sontarans (TV: The Two Doctors) and the Cybermen. (TV: Attack of the Cybermen)