| “ | "Cailin" means "uncertain." That's the name that my mother picked for me. "Maura" means "great." That's the name she picked for you. | ” |
–Cailin, "Money Maker" | ||
Cailin is the second child of Dr. Hope Martin and the younger half-sister of Maura Isles. She was raised in London and attended the University of Oxford before moving to Boston.
History[]
Hope seemed to have told Cailin about her stillborn child often since her childhood, although since Hope was a medical activist, she was often busy or away. At one point, Cailin contracted a bacterial infection while Hope was doing relief work in Africa. Unable to find a kidney to match hers, Hope moves to Boston with her. Since finding out, Hope has been trying to bond with her to make up for all the years she wasn't there, but Cailin has grown more distant and already accepted that she is dying.
Season Three[]
When they move to Boston, Cailin openly shows her contempt about Hope's decision to move there..
During an awkward dinner at Maura's with Hope, Jane, and Angela, Cailin goes snooping around in Maura's bathroom and finds Paddy's drawing of Hope. She then starts looking up Maura and finds out that her father is Paddy Doyle; she then connects Maura to Hope's dead daughter.
When Maura later finds out that Cailin needs a kidney, she decides to donate one of her own anonymously.
Later, Cailin returns to Maura's house and confronts her, telling her that she knows that she is her mother's daughter too. She tells Maura that she has lived in her dead shadow her whole life and she never seemed to be enough to fill the hole in her mother's life. Cailin also figures out that Maura was the anonymous donor of the kidney and she insists on refusing it, even if this means that she would rather die than have any part of Maura in her.
During the argument, Cailin also points out that she should have just told them the truth. So later, when Hope suddenly arrives, Maura tells Hope the truth out of nowhere, pressured by Cailin's breakdown. Cailin seems shocked at this, even more when her mother retreats from the scene with her, saying that Cailin is her daughter, and even seems reluctant to leave Maura in tears when Hope wants to leave, pulling Cailin with her.
Season Four[]
In episode 1, "We Are Family", it is revealed that despite Cailin's objections, Maura still secretly donated her kidney to Cailin. Upset, thinking that she and Hope were ungrateful, Maura tails her, hoping to find out how Cailin is treating her new kidney, and when Cailin sees her, she thanks her, admitting that she knows. She then gives Maura a letter and the scrimshaw necklace, the Doyle family heirloom that Hope gave her on her 18th birthday (which Hope had apparently received from Paddy on her 18th birthday), saying it belongs to her. Cailin then offers to keep in contact with her, asking if she can "text her" sometime, and Maura happily agrees.
In episode 2 "In Over Your Head", Cailin visits Maura and Jane at BPD. In the cafe', she tells them about men who came by her house last night, and her mom, Hope, told her to go to her room and lock her door. While she didn't hear everything they were talking about, Cailin overheard the men mention her mother's charity MEND (Medical Emergency Network of Doctors), and Cailin thinks the men were threatening her mom. Hope, following the discussion with the men, tells Cailin they're moving back to London, which Cailin is bummed about since she loves living in Boston now. When she mentions Boston is full of ghosts to Hope, Maura looks sad, but Cailin quickly clarifies that she was talking about Paddy Doyle, not Maura. She tells Jane and Maura that Hope has been following Paddy's RICO pre-trial hearings in the newspaper, but she is happy that Maura is wearing the scrimshaw necklace, which Maura responds that it was very sweet of Cailin to give it to her. Cailin then leaves to get to class, but she asks Maura and Jane if they can talk to Hope about the men, and Maura agrees. Later, Cailin texts Maura and tells her that the FEDs have left their house.
In episode 8, "Cold As Ice", Cailin comes to Maura's and tells her Hope went to Europe for three weeks, but she couldn't go with her because she had finals. She asks Maura if she can stay with her so she won't have to stay home with Mrs. Craberton, the babysitter Hope hired for her. Maura agrees, and Cailin thanks her. Cailin then heads off to find the spare guest room while talking to one of her friends on the phone. When she starts blasting music, Maura goes to talk to her while Jane heads off to the crime scene.
Later, Maura is so panicked when she can't reach or find Cailin that she files a missing person's report. Right after she does, Cailin comes home and reveals she was at the library studying and had her phone off. When she finds out Maura filed a missing person's report on her, Cailin is disappointed, as she thought Maura was different than her overprotective mother Hope, which makes Maura more upset. To help ease the tension, Angela tells Cailin that Maura doesn't have kids, and while Cailin is not a child, Maura is responsible for her well-being while Hope is out of the country. Cailin argues that sending the police on a wild-goose chase isn't responsible since they have better things to do, like solve a murder, and Maura hurts Cailin's feelings when she says she has better things to do than take care of an irresponsible selfish teenager. Angela scolds Maura for saying that, and tells Cailin that Maura was only worried about her. When Angela offers Cailin a brownie, she jokes that she'll only have one if they have marijuana in them, since growing marijuana is something only a irresponsible selfish teenager would do. Angela quickly clarifies to an angrily Maura that Cailin is kidding, then Angela sends Cailin to take a bath to help her de-stress from studying for her finals, and she promises to bring Cailin a cup of tea in a little bit. After Cailin exits, Maura tells Angela she never gets that angry, and Angela tells her it will be OK, since that is what a fight with a sibling feels like.
The next morning, Maura comes downstairs and finds out Cailin invited some friends over, pulled an all-nighter and made a mess of her kitchen while making breakfast. Cailin tells Maura she can go take a shower if she wants. Maura asks if she's embarrassing her, but one of Cailin's friends says she looks great for her age, which Cailin has to clarify that it's a compliment. Maura wants to speak to Cailin privately, but the talk gets delay when Cailin reveals that she made Maura and Angela breakfast. And after Angela encourages Maura to set some boundaries with Cailin, Maura tells Cailin that she would like Cailin to clean up after herself, and Cailin says she will after her class.
Later at the police station, after Maura tells Jane what happened, Jane points out that Cailin is a good person and a good student, and asks Maura if she needs to be a good cleaner too. At first Maura says no, but then says yes. Then in the BPD cafe, after Jane finds out Maura told Cailin that she needs to keep in contact with her every thirty minutes, Jane says that Maura is the one causing problems since she is treating Cailin like a kid. Jane reminds Maura that Cailin came to her as a big sister, not as another mother, then she encourages Maura to give Cailin a sisterly relationship, the very thing Cailin is after.
At the end of the episode, Cailin comes home while Jane and Maura are drinking wine. Cailin guesses that they won't offer her a glass of wine, though Maura does offer that they could pretend it's France. Cailin then jokes about knowing a guy who can get her a six-pack, then offers to cook Jane something. When Maura asks if she plans to clean up afterwards, Cailin asks if that's part of the deal, Maura then says no. Jane then proposes that they order takeout and Cailin can help her throw out the boxes. Cailin agrees, and so does Maura, who is happy about the compromise.
It is implied that they have a good sisterly relationship afterwards.