The Doctor (David Tennant) and Donna Noble (Catherine Tate) arrive in what the Doctor believes to be first century Rome. After an earthquake, he realises he has materialised in Pompeii on 23 August 79, one day before the eruption of Mount Vesuvius. When he returns to the TARDIS' location, he is told it was sold to a Lucius Caecilius Iucundus (Peter Capaldi), a marble sculptor.
The episode's antagonists are the Pyrovile, giant rock-like creatures resembling golems whose home planet was "lost". They operate secretly; the Sybilline Sisterhood act as their proxies. They use the Sisterhood, which incorporates a high priestess (Victoria Wicks), Spurrina (Sasha Behar), and Thalina (Lorraine Burroughs), to make prophecies while converting them to stone. The Sisterhood is inducting Caecilius' daughter Evelina (Francesca Fowler) and is allied to the local augur Lucius (Phil Davis). The Doctor is disturbed by their knowledge of his and Donna's personal lives, and by Lucius' latest commission, a marble circuit board.
The Doctor breaks into Lucius' home and discovers that he is creating an energy converter. He is accosted by Lucius, who sends a Pyrovile to kill the Doctor. The confusion allows the Sisterhood to kidnap Donna briefly; the Doctor follows them and frees Donna. They escape into the Sisterhood's hypocaust system and travel into the centre of Mount Vesuvius.
Mount Vesuvius is being used by the Pyrovile to convert the human race to Pyroviles. The Doctor realises the volcano will not erupt if the energy converter is running, and subsequently switches it off, triggering the eruption of Vesuvius. The Doctor attempts to leave, but Donna convinces him to save Caecilius' family, whom he then takes on board the Tardis. The family, The Doctor, and Donna then watch Pompeii's destruction from a vantage point. The Doctor assures the family that Pompeii is never forgotten before leaving with Donna.
The last scene takes place six months later in Rome. Caecilius' family are shown to be successful: Caecilius is running a profiting business, Evelina has a social life in comparison to her seclusion in Pompeii, and his son Quintus (Francois Pandolfo) is training to become a doctor. Before Quintus leaves, he pays tribute to the family's household gods, whose statues are in the form of the Doctor and Donna.
Doctor David Tennant (Tenth Doctor)
Companion Catherine Tate (Donna Noble)
Peter Capaldi – Caecilius
Tracey Childs – Metella
Phil Davis – Lucius
Sasha Behar – Spurrina
Francesca Fowler – Evelina
Lorraine Burroughs – Thalina
Victoria Wicks – High Priestess
Francois Pandolfo – Quintus
Karen Gillan – Soothsayer
Phil Cornwell – Stallholder
Writer James Moran
Director Colin Teague
Script editor Brian Minchin
Producer Phil Collinson
Executive producer(s) Russell T. Davies
Production code 4.2
Series Series 4
Length 50 minutes
Originally broadcast 12 April 2008