Sonila Vjeshta from "Vampires of Venice"
The Doctor, believing Amy's attraction to him is due to the stress from travel, gatecrashes her fiancé Rory's stag party, and invites the two of them on a romantic trip courtesy of the TARDIS. They land in Venice of 1580, but soon find that the city's patron Signora Rosanna Calvierri claims (falsely, according to the Doctor) that a plague runs rampant outside of Venice, which she is using as an excuse to seal off the city. When they try to learn more from Signora Calvierri, they encounter Guido, a boat-builder, desperately seeking information on his daughter Isabella. Guido explains that Signora Calvierri runs a highly-praised school for the betterment of young ladies, which he was able to enroll Isabella into, but now fears something is wrong with the school. The Doctor, and Amy and Rory separately investigate; they all come to the same initial conclusion: Signora Calvierri, her son Francesco, and the girls in the school are all apparently vampires, feeding on the blood of young women by biting their necks with long teeth, fearing direct sunlight, and leaving no reflection in a mirror.
Amy devises a plan to place herself within the school with the help of Rory, whereupon later she can allow in Rory and the Doctor through a canal entrance assisted by Guido. Though she is able to unlock the necessary gate, Amy is discovered by the other girls in the school and taken to a chamber to be turned into a vampire; in her struggles, she kicks at Signora Calvierri to find her wearing a device that masks an alien form underneath. The Doctor and Rory arrive in time, and with the help of Isabella, who has yet to be converted, free Amy and escape the school; however, Isabella is caught at the last moment while helping in the escape as she can't handle the sunlight; the Doctor tries to open the door but he gets shocked by electricity and he collapses. Isabella is later thrown into a canal by Signora Calvierri and eaten by something that lives underwater.
The Doctor decides to address Signora Calvierri directly, and confirms that she and the others are creatures from the planet Saturnyne, a race of aquatic beings with vampire-like tendencies, but wearing perception filters—the device Amy struck—to make them appear human and the cause for lack of reflection in the mirror. Signora Calvierri states they were fleeing from numerous cracks in time that threatened their planet, through some of which they heard only silence on the other side. Calvierri and her son fell through one crack into Venice, and are now seeking to sink the city and convert humans into "Sisters of the Water" in order to continue their race. When the Doctor returns to Guido's home to report this to the others, Signora Calvierri sends her girls to attack them. Guido sacrifices himself for the others by blowing up several kegs of gunpowder that kill him and the girls. Signora Calvierri activates a device on the top of a tower that begins to create earthquakes and tsumanis that will sink Venice. While Amy and Rory face and defeat Francesco, the Doctor climbs the tower and stops the device in time. The last of her kind, Signora Calvierri throws herself into the canal where her doomed offspring await, but not before tormenting the Doctor that he is now responsible for the extinction of two species: her own, and the Time Lords.
In the aftermath of the incident, Amy and the Doctor invite Rory to continue traveling with them in the TARDIS, but as the Doctor and Rory are about to enter the TARDIS, everything falls silent. Unnerved, the Doctor remembers Signora Calvierri's words: "We saw silence, and the end of all things..."