Fiona Helbron

Fiona "Mittens" Helbron is a recurring character in the American crime series Elementary.

Early life
Fiona works as a lead programmer at Pentillion Edge, a large R&D firm. She has a reputation of being weird.

Murder ex Machina
Fiona is first introduced to the viewers as a programmer whose code was used in a multiple murder. Though she is initially a suspect, it quickly becomes clear that she wouldn't hurt a fly and combined with her inability to lie, the suspicions are cleared. Further along in the investigation, Sherlock realizes that Fiona's boss, Balsam, is behind the killings, and asks Fiona's help to apprehend him. They overtake his car with her software and are able to get a confession from him.

A View with a Room
This time, it's Fiona who needs a detective. She wants to meet up with just Joan Wattson. She is afraid that her new boss Greg Wakino will turn out like Balsam and also use her code to hurt people, which she really doesn't want. Wattson finds that Wakino is genuinely a great guy (smart, patient, boards two charities), and though Fiona is not entirely convinced, Wattson assures her that he gives her good vibes. Fiona also gives back a rare, first edition book with poetry about cats that Sherlock loaned her. Wattson deduces that Sherlock is in love with her, since there are exactly 0 poetry books at Sherlock's house so he must've gone out of his way to buy the book specifically for Fiona. Wattson encourages him to pursue Fiona, but he's afraid he'll hurt her (or that she'll hurt him like his previous lover did).

Fiona comes to Sherlock's house to give Wattson a thank you gift, and confesses to Sherlock that she likes talking to him. They talk a bit and she ends up confessing her love for him, though their moment together is interrupted by his phone ringing. Later Sherlock visits her at her home to pick up where they left off. She talks about how her previous boyfriends said that she's a lot of work. Sherlock would like to kiss, but Fiona declines for the time being, asking him out for coffee instead.

Ready or Not
Fiona visits Sherlock's house, but Wattson informs her that he's out. Fiona has something to say but she'll come back later.

Later, Sherlock talks to Wattson about his relationship with Fiona. They're taking it slow and haven't had sex yet, which is making Sherlock a bit antsy since he usually has lots of casual sex, but he's willing to put in the extra effort for Fiona. He's also done research on relationships with autistic people.

Fiona texts him to meet up at his place. She tells him that she feels he's not acting like he did when they first dating and instead acts like he thinks he's supposed to (that is, too careful). She feels like a project or problem to be solved, and breaks up with him. Sherlock invites her back to talk things over; he explains that he puts in extra effort not because she is different, but because he is different and relationship are hard for him, and because he believes she is worth the extra effort. They then have sex.

Ill Findings
Fiona is on a business trip to Philadelphia for the past month and video chats with Sherlock. She wants to spend time with him and invites him to Cranbury Township, New Jersey, as it is exactly halfway between Philadelphia and New York.

In the meanwhile, Sherlock realizes that he and Fiona don't talk about their jobs. While discussion this with Wattson, he laments how it's not the same as his previous relationship with Moriarty. Later, Wattson gives him some advice about break-ups, sensing that he might want to separate from Fiona but doesn't know how. Sherlock repeats the advice Wattson gave him about break-ups to himself right before a video call with Fiona.

Autism
Fiona confirms herself to be autistic on her first appearance, though she prefers the term neuroatypical. "They say autism is a spectrum but it's really an array of different conditions all lumped together. I prefer the term neuroatypical, it's more accurate."

- Fiona

She immediately clocks Wattson as neurotypical, but can't quite put her finger on exactly what Sherlock is.

Episode list
Elementary
 * season 4, episode 9: "Murder ex Machina"
 * season 4, episode 12: "A View with a Room"
 * season 4, episode 18: "Ready or Not"
 * season 5, episode 6: "Ill Tidings"

Trivia

 * Fiona is a big fan of cats, hence the nickname "Mittens". Her apartment doesn't allow pets, so she often visits a nearby cat café.
 * Sherlock loaned Fiona a 1939, first edition of Old Possum's Book of Practical Cats by Thomas Stearns Elliot. Sherlock figured she might like poems about cats, seeing as she likes cats so much. She didn't like the poems. The book is also the inspiration for Andrew Lloyd Webber's musical Cats.
 * Fiona thinks that Sherlock smells nice.
 * She has had 2 boyfriends before dating Sherlock, both neurotypical.
 * Sherlock bought Fiona a cat, Miss Purrdy, for her birthday, but the cat did not like her so Sherlock had to take her back. Ms. Hudson takes her in, but the cat doesn't like her either, so Sherlock ends up putting Miss Purrdy up for adoption.
 * Wattson believes that Sherlock broke things off with Fiona because she doesn't compare to his previous relationship with Moriarty.