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They say autism is a spectrum, but it's really an array of different conditions all lumped together.

— Fiona, "Murder Ex Machina"

Fiona Helbron is the lead computer programmer for Pentillion Edge. She dates Sherlock Holmes, is autistic (neurodivergent) and likes cats.


Season 4[]

S04E09-Fiona at work

"I like it when the code works."

Joan Watson and Holmes question Fiona and her boss Phil Balsam after discovering that her code for operating a driverless car was used to kill two Ukrainian hitmen. They discover that the code was stolen and Fiona is incapable of lying. Holmes later suspects her boss of being behind a drive-by killing perpetrated by the hitmen and with Fiona's help, Balsam's car is overtaken by Fiona and Holmes is able to get a confession from him.[1]

Fiona asks for Watson's help assessing her new boss. Later, when Watson delivers her report to Fiona she gives Watson a book that Holmes lent her and Watson realizes that he likes Fiona. Watson teases Holmes about this which makes him uncomfortable. Fiona visits the Brownstone with thank you gifts for Watson but really wants to see Holmes. They go on the roof and she declares her interest in Holmes which genuinely astonishes him. His phone rings which interrupts the moment. Later, Holmes visits Fiona at her apartment where she tells him she's had boyfriends before, but they said she's a lot of work. Holmes asks if can kiss her but she's scared and asks him out for coffee.[2]

S04E18-Fiona Sherlock kiss

"I think we should have sex now."

Fiona drops by the Brownstone unexpectedly when Holmes isn't there. She tells Watson she has prepared something to say to him and will come back later. Holmes tells Watson he and Fiona haven't had sex and he's trying hard to be respectful. When Fiona talks to Holmes, she says that she feels that he's being too careful and views her as a problem to be solved and she's breaking up with him. Later, Holmes convinces Fiona to come back to the Brownstone and explains to her that the extra effort he's been making is because he is different and he tells her about his one past relationship. Impressed, Fiona says she wants have sex with him.[3]

Season 5[]

S05E06-Fiona skype

"I wasn't sure you'd say yes."

Fiona and Holmes talk via video chat as she's working in Philadelphia. He accepts her offer to meet for the weekend at a bed and breakfast in New Jersey. As Holmes talks to Detective Bell and Watson about relationships, he realizes that he doesn't talk about his work to Fiona. Watson quotes from Shakespeare regarding how to break bad news. Later, before Holmes takes a video chat with Fiona, he recites the quote, implying that Holmes broke up with Fiona.[4]


  • Her love for cats is well known in the coding community, and Mason was able to identify her based on her signature as "Mittens."[1]
  • Holmes is the third person Fiona has dated.[2]
  • Holmes bought a cat for Fiona's birthday, Miss Purrdy, but the cat doesn't take to Fiona. Ms. Hudson offered to adopt Purrdy, but things did not work out between them so Sherlock had to put an adoption notice online.[5]
  • After Holmes complains that Harland Emple continually pines over an unattainable woman, Watson points out to Holmes that he does the same thing with Moriarty. She also believes that he broke up with Fiona because she didn't compare to Moriarty.[6]


  1. 1.0 1.1 Season 4, episode 9: "Murder Ex Machina"
  2. 2.0 2.1 Season 4, episode 12: "A View with a Room"
  3. Season 4, episode 18: "Ready or Not"
  4. Season 5, episode 6: "Ill Tidings"
  5. Season 4, episode 21: "Ain't Nothing Like the Real Thing"
  6. Season 6, episode 19: "The Geek Interpreter"