The Doctor (Matt Smith) feels that his companion Amy Pond (Karen Gillan) kissed him in the last episode because she is under stress, so he crashes the stag party for her Fiancé Rory (Arthur Darvill) and invites the two of them to romantic Venice in 1580. The city’s patron, Signora Rosanna Calvieri (Helen McCrory), has sealed Venice because the plague is raging outside the city, but the Doctor knows this is not so and wonders what she’s up to. They encounter a boat-builder named Guido (Lucian Msamati) whose daughter has not contacted him since enrolling in Rosanna’s school for girls.
Amy sneaks into the school and when she unlocks the gate to allow the others in, she is captured and taken to a chamber. The Doctor and Rory figure out that the girls are being changed into vampires. Amy kicks Rosanna and breaks a device that is hiding her fishlike alien form. Before they can finish converting Amy, Isabella (Alisha Bailey) frees her, and they escape the palace. Isabella hesitates because she cannot stand sunlight and is pulled back inside. She is thrown into a canal and eaten by something in the water.
The Doctor questions Rosanna, who admits that her species arrived on Earth from the planet Saturnyne after seeing “silence and the end of all things.” Rosanna was the only female of the race to survive the trip. She and her son Francesco (Alex Price) want to sink Venice into the water and convert girls into fish-creatures to save their species.
When the Doctor returns to Guido’s home to join Amy and Rory, Rosanna sends the converted girls to attack them. Guido uses gunpowder to kill himself and the girls. Amy and Rory defeat Francesco, the Doctor stops the device sinking the city, and Rosanna—last of her kind—throws herself into the canal to be eaten. Just before the time-travellers enter the TARDIS, silence falls over the city.
The story was filmed in Trogir, Croatia, because Venice was too modern. The interior of the Calvieri house was filmed at various places, including the Castell Coch in the UK. Computer generated water turned a street into a canal. Some scenes were cut, thought to be too scary. The episode received mixed reviews. The adventure and the humour were appreciated, but the plot was called too derivative and too similar to other Doctor Who episodes.
When the Doctor tries to show his psychic paper, he pulls out a library card with William Hartnell’s picture on it. The vampire teeth were molded to fit each individual actor, but it was still hard to talk with them in. McCrory did a good job of moving like a fish. She and Alex Price play mother and son here, and in the Harry Potter universe, McCrory played Narcissa Malfoy, while Alex Price in a play was Draco. Rory and Amy were amusing together, the vampires were creepy, the sets impressive, and Helen McCrory pretty much ran away with the episode.