|Portrayed by||Ophelia Lovibond|
|First seen||"Enough Nemesis To Go Around"|
|Last seen||"The One That Got Away"|
|Born||(c. 1986) (28 years old)|
|Occupation|| Transcriptionist (? - 2013)|
Protégé turned partner of Sherlock Holmes (2013 - 2014)
|Residence||The Brownstone, Brooklyn, New York City, New York, U.S.|
|Spouse(s)||Unnamed ex-boyfriend (father of child)|
Katherine "Kitty" Winter Sherlock's new protege, she worked with Sherlock in London and moved with him to New York. Kitty helps Sherlock with his cases and learns his methods.
Five years before gaining the acquaintance of Sherlock, Kitty was kidnapped, raped and tortured by a male perpetrator. She now lives under an assumed identity in an attempt to escape her former reality. Kitty admits to Joan Watson that she was at a low point in her life before meeting Sherlock in London. After becoming Sherlock's protégé, essentially assuming Joan Watson's role, she follows Sherlock to New York City and resides in The Brownstone with him. Within weeks of living in the city, she gains an interest in Joan Watson; even after her surveillance of Watson was ordered to be discontinued, she persists anyway and unintentionally confronts Watson in a fight of Singlestick. Although initially having felt rivaled by Watson, Kitty begins to realize that her capabilites may be better enhanced with the assistance of Joan. Being a rape victim, she accepts Joan's recommendation of attending regular support groups, as a means of indicating her compliance with Joan. However, Kitty tells Joan that she is only doing this to fulfill her potential, just as Joan did when she was being mentored by Sherlock. In the last episode, Kitty appears back in New York and admits she has a son, named Archie.
- Kitty Winter is a character in the canon Sherlock Holmes short story, "The Adventure of the Illustrious Client" by Sir Arthur Conan Doyle.
- This is further alluded to in the second last episode she appears in, titled "The Illustrious Client"