Gwen and Olivia Lynch are identical twin sisters living in New York City.
Background[]
They have a semi-frequent sexual relationship with Sherlock Holmes, who describes their interaction as "mutually beneficial": their contact allows him to study the differences between two people who are otherwise genetically identical (according to him, there are seven major differences between the Lynch Sisters). As to what they get in return, Joan Watson cut him off before he could explain, but both sisters bid a fond farewell to Sherlock when they departed The Brownstone after their last rendezvous.
Apart from their respective clothing, the sisters can be told apart by the fact that Gwen wears glasses, while Olivia does not.
Trivia[]
The Lynch Sisters are actually played by a single actress, Tonya Glanz.