Joan McGarrett

Joan McGarrett is the adopted daughter of Mary McGarrett and niece of Lieutenant Commander Steve McGarrett.

Season 4
In Ua Nalohia, Joan is first seen on Steve's doorstep with a note attached to her front that reads, “Congratulations, it's a girl” Steve looks around in confusion, before crouching down to the baby's level. Mary jumps out with her phone at the ready to capture the look on Steve's face on camera. Steve stands up and asks her whose baby is it. To which Mary replies it's hers. Steve doesn't believe her, but Mary says she adopted the baby. Mary says the adoption’s been in the works for awhile but she kept on the down low in case Steve was critical about it. Mary says she named her after their dad, and called her Joan. As Steve leaves for work, Mary waves Joan's hand at him and says bye.

When Steve tells Danny about Joan, Danny tells him that Mary didn't adopt a kid, Steve did, and it's only a matter of time before Steve will have to look after her. Steve says that won't happen because the baby is going back. Danny asks if Steve's going to send Joan back to the orphanage, with the other kids that nobody wants.

Steve asks him whose side is he on, Danny says he's on the side where the kid gets a chance to be loved and if Steve thinks that Mary is capable of doing that, then he's all for it.

Mary is later admitted to the hospital for salmonella poisoning and she needs to stay overnight, she asks Steve if he'll watch Joan for her. Steve says he can't do that, but Mary pleads with him that she doesn't have anyone else to call. Steve tells her that he is in the middle of a homicide investigation. Mary said okay and that she'll just have to contact Child Protection Services and get Joan placed with a foster care family for a while and calls Steve a horrible uncle.

Steve is then seen entering headquarters with a baby bag and Joan strapped to his chest in a baby carrier. Danny laughs at him when he enters. When Steve asks if he'll help with the diaper changing mat, Danny says he's retired from babies and watching Uncle Steve try is going to be amusing. Chin walks over and asks why is there a baby strapped to Steve's chest and Danny just says “Mary”. Chin says “Say no more”.

Steve unstraps Joan from his chest, as Chin explains that he tracked down the key they found. Steve asks to see the key and tells Chin to just hold Joan for a second. As soon as Chin has Joan, Steve tells Danny that they're going. Chin is shocked and looks scared as Steve tells him that if she gets hungry she has a bottle in the bag. He asks how will he know if she hungry, Steve says he’ll know and leaves with Danny. Chin holds Joan away from his body, under her armpits.

After Danny and Steve get back, Chin comes back out of an office with Joan, he has baby throw up stains on his shirt. Steve takes Joan back, and amuses her while Chin tells them what he found. Danny asks Steve to focus, but Steve prove he can multi task by repeating what Chin found. Steve then passes Joan off to Danny and Danny asks him what's he doing. Steve replies that they're a team and that it's his turn. Danny sits Joan on the computer desk and she grabs a bundle of money to play with. Steve tells him to not let her drool on the evidence. Steve mentions that her diaper needs changing soon and leaves with Chin.

Danny takes Joan to his office and tells her a story to entertain her, the story based on Danny and Steve's battle for control of Danny's car with a fairy tale twist. Danny then takes Joan with him to meet with the real estate agent.

When Steve comes to meet Danny, he tells Danny that if he's going to take the baby out in the sun just ask and he'll put her sunhat on. Steve then swaps Joan's pink beanie for a yellow sunhat.

Back at headquarters, Steve is holding Joan with one arm. As he talks he places Joan on the computer desk, but she tries to crawl across it. He stops her from crawling around on the computer by picking her up again. Steve leaves with Joan in his arms and Danny asks what's he doing. Steve says he's going to finish what Matt started and then asks Joan if she wants to come. Joan is left with Max while Steve runs his operation.

Later that day Mary is out of the hospital and is at headquarters. Steve returns Joan to her. Mary comments that Joan's got no dings or scratches, so that means that Uncle Steve did a good job. Mary tells him to admit that he had some fun and she knows who she'll be calling if she needs a babysitter, nodding to Danny and Chin. Steve says it was a team effort and they all contributed and that he was the primary on the op, Mary just laughs at him. Steve says that they've just finished a case and invites her and Joan to celebrate with the team but Mary says that she and Joan have "Bouncing Baby Story Time" at the library. Mary waves Joan's hand as she says goodbye to uncle Steve, uncle Danny and uncle Chin.

In Ha'uoli La Ho'omoaika'i, Joan is at Steve's house in her high chair watching Mary try to defrost a turkey with a hairdryer. She is then introduced to her Great Aunt Deb who has come to visit.

Aunt Deb, Mary and Joan then go to the local butcher to see about getting another turkey for dinner. The butcher tells them they've got to be kidding as it's Thanksgiving but he'll go out back and have a look. Joan then begins to fuss, Mary tries to settle her but is unable to do so. Aunt Deb takes her, and Joan settles quickly. Mary looks on in awe and says that Aunt Deb is some kind of baby whisperer and asks her to send some of that her way. Mary then confides to Aunt Deb that she feels like she's in over her head and she's got no clue what she is doing. Aunt Deb tells her that she was winging it the whole time she was raising Mary and it was scary. Being a mom is the hardest job in the world, but she couldn't think of anyone that was better suited for it than Mary. Mary's got a big heart, she is smart and all she has to do is love Joan with everything she's got and she'll be fine.

Joan is with her family and their friends when they have to use Steve's back up dinner plans. Turns out Steve's back up plan is to have dinner at the La Mariana Tiki Bar. The group enjoys a song sung by Aunt Deb.

Season 6
In Ua Ola Loko I Ke Aloha, Joan is with her mother and uncle, as they watch Deb says goodbye to her late husband. She also watches when Kawika takes the ashes out to be spread across the ocean.

Joan gets to ride in the backseat of Steve’s truck when Deb takes it for a spin. She has the time of her life, happily yelling and when Mary mentions that it looks like Steve is going to puke, she repeats ‘puke, puke, puke’ over and over again. Steve tells Mary to make her stop, but Mary ignores him and laughs with her daughter.

Later in the day Joan, Mary and Deb go on an epic shopping spree to cross off another item off of Deb’s bucket list. When they finish shopping Mary takes Joan with her as she goes and get the car.

The next day, Joan is in her highchair in Steve’s kitchen, Mary is cooking pancakes and Steve is telling when to flip them. As Steve leaves to wake up Deb, he tells Joan to watch her mom, as Mary is likely to burn the house down with her cooking. Mary then tells Joan not to listen to Steve and kisses her head.

Joan, Mary and Steve climb to the top of a really tall mountain and spread Deb’s ashes, completing the last thing on Deb’s bucket list.