Madame Vastra

[close] was a Silurian detective who shared a house at 13 Paternoster Row with Jenny Flint, her maid and eventual wife, in Victorian London. Alongside Jenny and the Sontaran nurse Strax, Vastra investigated unusual activities. Vastra employed Strax as a butler in London while Jenny became the maid to cover any possible gossip.
In the 1880s, Vastra had awoken during the construction of an extension of the London Underground and sought to take revenge on the innocent tunnel workers responsible for the accidental deaths of her "sisters". After Vastra had slaughtered at least five commuters, the Ninth Doctor convinced her not to give in to her rage. At the Doctor's insistence, she ceased her attacks on the tunnel workers and instead integrated herself into humanity's Victorian culture.
Vastra gained the title of "Madame" and took up residence at Paternoster Row. She eventually became a detective and consultant to Scotland Yard, solving cases that they could not. Due to her proficiency in the field, some referred to her by the title of "the Great Detective".