The Doctor and Ace arrive at Earth some eight hundred thousand years in Ace's future. He tells her that at this point the Earth has been deserted. From the monitor, they see something strange in what used to be Prague: the street layout spells out an SOS — in Gallifreyan.
The Doctor tells Ace that the streets were planned in 1348. They decide to investigate.
Thought the planet is supposed to be deserted, they encounter two men who are clearing the road. The Doctor realises they are John Dee and Edward Kelley. They claim to have been brought here by an Angel. Kelley threatens the Doctor with a knife and takes them to the "Angel".
They are taken to see Uriel, who is overjoyed to see another Time Lord. He explains that he's been in Prague since 1380 and has no idea how Dee and Kelley got here. His TARDIS was destroyed during an emergency landing, so he insinuated himself into Prague aristocracy. It was he who planned the SOS road design. In 1586 he met Dee and Kelley, who just disappeared one day. In 1591, a Time Lord rescued him and brought him to this place; when he arrived he found Dee and Kelley. He's been here for five years.
Though Ace doesn't trust Uriel, they take the three men to the TARDIS. After a short time, Uriel grabs Kelley's knife and orders the Doctor to dematerialise. He knocks out Dee and Kelley and forces the four out of the TARDIS, which then leaves.
Suddenly Ace and the Doctor hear the TARDIS arrive. Another Doctor asks if Uriel is gone, to which the Doctor replies he has. The new Ace and Doctor drag a new Dee and Kelley out of the TARDIS, go back inside and depart.
Before Ace can finish a question, the TARDIS arrives again. This time, a different Uriel emerges. He is surprised to see the unconscious Dee and Kelley. While he stares at them, the Doctor and Ace sneak into the TARDIS and depart.
The Doctor explains to Ace what has happened. When Uriel forced the TARDIS out of the time stream, it was five years earlier. The Doctor had programmed the TARDIS to 1591, so it took Uriel to that time. When he arrived there, the original Uriel from 1591 took the TARDIS to where the Doctor and Ace were waiting. For five years Uriel, Dee and Kelley will clear the roads so the SOS will be visible from space.
When Ace asks how Dee and Kelley arrived in the future, the Doctor realises that he must take them out of 1586, at the time they just disappeared. Once they retrieve the pair, they take them to the far future, depositing them there while being watched by their original selves. They take the other versions of Dee and Kelley back to 1586 a few days after they disappeared.
- The Doctor thinks Uriel is a Raagr'an from somewhere near Betelgeuse.
- Ace is trying without success to read Moby-Dick.
- Kelley's ears have been removed as a punishment for forgery.
to be added