The Tenth Doctor and Donna arrive in Pompeii the day before the eruption of Mount Vesuvius in 79. They later discover a local merchant has sold the TARDIS to sculptor Lobus Caecilius. The Doctor and Donna go to Caecilius’ house to retrieve it. Unknown to them, they have been followed by a soothsayer who reports to the Sibylline Sisterhood that the prophesied man in the blue box has arrived, and the Sisters fear the prediction that his arrival brings fire and death.
The circuit prop, on display at the Doctor Who Experience
At the house, the Doctor and Donna meet the local augur, Lucius Petrus Dextrus, who has arrived to collect a sculpture he commissioned. The Doctor is intrigued by the sculpture, which resembles a segment of an oversized circuit board. The Doctor wishes to learn more about the sculptures and enlists Caecilius’ son Quintus to help him break into Lucius Petrus’ house. Inside, the Doctor deduces that the circuits will make an energy converter, but he is caught by Lucius Petrus, who beckons a large stone creature to attack and kill them. The stone creature appears in Caecilius’ house and attacks them, but Quintus douses the creature in water and kills it. In the confusion, the Sisterhood kidnap Donna, and the Doctor sets off to rescue her. The Doctor discovers that the Sisterhood are being controlled by the Pyroviles, stony creatures whose home planet of Pyrovilia was lost. The Doctor escapes with Donna into a tunnel that leads into the heart of Mount Vesuvius.
The Doctor discovers that the volcano is being used by the Pyroviles to convert the human race and conquer Earth. The Doctor realises the volcano will not erupt if the energy converter is running, and tells Donna that the volcanic eruption is a fixed point in time and must always happen. The Doctor and Donna get into an escape pod and together press a lever which overloads the converter and triggers the eruption, killing the Pyroviles and launching the pod clear of the blast. The Doctor and Donna run for the TARDIS, leaving Caecilius and his family behind in their home. However, Donna tearfully begs the Doctor to go back and at least save one person from the volcano. The Doctor relents and goes back for Caecilius and his family, leaving them on a hill to watch the destruction. He comments to Donna that she was right – he does need someone to stop him.
Six months later, Caecilius’s family are living happily away from Pompeii. Caecilius’s son, now training to be a physician, gives his thanks to the household gods by throwing blessed water on a relief on the wall, revealed to be an image of the Doctor and Donna, standing next to the TARDIS.