The Esturians were a race of liquid beings. They travelled between worlds abducting children and transforming them into underwater servants.
In 1897, two Esturians landed their spaceship in the River Thames. Vastra, Jenny Flint, and Strax investigated the spaceship after the Esturians kidnapped four children from an orphanage. Strax used a Sontaran liquid storage device to trap the Esturians. After taking the Esturians to 13 Paternoster Row, Strax accidentally dropped them into the house's water tank. They were killed when Vastra heated some water to make tea. (PROSE: The Terror of the Thames)