Casey Gardner and Izzie Taylor meet when Casey transfers to Clayton Prep. When they first meet, Izzie is shown to be rude to Casey and does not seem to like her, since she heard that Casey punched Bailey Bennett in the face at Newton High School. They later get on really well while in detention, after realizing they both have things in common. However, Izzie pushes Casey away, because of an incident with Nate (Izzie's boyfriend). Later in Season 2, Izzie goes up to Casey's room during Casey's 16th birthday party to apologize for the way she has been acting, wanting to be friends again and says "let's forehead promise, to never leave each other again." They put their foreheads together and lean in for a kiss. However, they are interrupted by Casey's mother, Elsa Gardner. In the last episode of Season 2, Casey and Izzie meet up and are sitting in Casey's car. The two hold hands, while sitting there silently.
In Season 3, their friendship progresses, and eventually, Izzie tells Casey that she likes her during a sleepover at Casey's house. Casey doesn't know how to react to this, and avoids Izzie for the whole day after the confession. The confession affects Casey's running performance, and she is sent home by her coach, so she can be better tomorrow. Later that evening, Casey goes out to the Clayton Prep running track, and Izzie finds her. Izzie is really upset, saying that she would have never told Casey that she liked her if she knew that their friendship would end. While Izzie is standing in front of Casey, very upset, Casey kisses her. This quickly turns into a passionate make-out session in the seventh episode.
Casey and Izzie are dating, but Izzie shows to be uncomfortable with the relationship, but only when her and Casey are around people (possibly due to internalized homophobia). After pushing away Casey once, she apologizes in ninth episode and she tells Casey that she wants to take it slow, because it's still all very new to her. After this, her, Casey and Sharice go to a party at one of the Newton Track Team member's room. At the party, the two dance very closely (almost provocatively) with each other, but as they are about to kiss, Izzie pushes Casey away, saying that she said they should take it slow. Casey is hurt and confused by this and becomes even more so when she sees Izzie talking to a guy, kissing him in the corner of the party.
Casey avoids Izzie at school and during track, including the competition, even though Izzie approaches her multiple times. However, they eventually make up. At the same time, Casey is called into Coach Crowley's office, as due to her outstanding performance in the race, UCLA have their eye on her. Due to how hard it is to get into UCLA, Coach Crowley says that Casey must 'eat, breathe and sleep track', and cut off all distractions (including Izzie), but Casey is unsure.
When Casey steps out, Izzie asks her what Coach wanted to talk about, but Casey lies and says that Coach just wanted to congratulate her on her performance in the race. Eventually, after accepting to devote her full focus to track, Casey comes clean and tells Izzie about UCLA and Izzie apologizes properly this time, saying that she knows that dating her isn't easy and that she understands if Casey doesn't want to be in this relationship anymore. Casey replies that she never wanted for easy, and they kiss passionately in Clayton's hallway, outside Coach's office, which soon turns into a mini make-out. After, they walk hand-in-hand through the hallways, implying that even though Casey is going to focus her attention on track, she's going to continue making time and dating Izzie.
Casey meets Izzie on her first day at Clayton Prep after transferring from Newton High School. Izzie is far from welcoming. When they first meet, Izzie is shown to be rude to Casey. stating she knows what happened at Casey's last school and what she heard wasn't good. Izzie says she doesn't want any drama, which Casey agrees with before Izzie leaves her to fend for herself instead of showing her around like the coach had expected. Even though Izzie was rude, later on at track practice, she is shown to be a little sympathetic towards Casey asking if she made her way around alright. Izzie also notices the state of Casey's trainers when a team member points it out and doesn't join in with the rest of the team when they laugh at Casey's comment about going to Target during the summer.
Later on in the episode, as Casey becomes friends with a boy called "Nate", who is revealed to be Izzie's boyfriend, he explains how Izzie is threatened by Casey, because she is faster than her.
Izzie and Casey are at track practice when they begin to race one another after Izzie makes a comment about Casey slowing down. They both begin sprinting down the track when Izzie falls and injures her wrist, falsely accusing Casey of tripping her up. They both end up getting detention because of this.
In Coach Crowley's office, Casey and Izzie are told by Coach Crowley that they are not to leave until they get along. After Coach Crowley leaves, Izzie asks Casey to get her phone because of her injured wrist still blaming her for the incident. Hearing Izzie mention a baby whilst on the phone, Casey asks if Izzie has a child, which reveals she looks after her three younger siblings at home; one of which is a baby. With this in common, it allows Casey to open up about Sam being autistic and they are finally able to bond.
As they open up to each other, Casey admits she doesn't think she will get out of the town, because her dad and Sam need her around. Izzie steps out the room for a second coming back with a bottle of Vodka she stole from a teammates locker, stating she's tired of being perfect constantly and suggests they stop caring about everyone else. They share the vodka when Izzie opens up that she spends so much time with Nate, because she doesn't want to go home and things don't feel quite right with him. This is the first sign of Izzie's possible sexuality. Casey, however, stated she doesn't feel that way with Evan.
Izzie walks up to Casey, saying she needs her because her mother's ex-boyfriend has moved back into the house before asking where Casey has been. She puts it down to life stuff to begin with before opening up about her father's panic attack, which they assumed was a heart attack. Izzie jokes that it's a miracle they are still alive before being interrupted by Nate.
Walking in to join Nate and Izzie, Casey complains about still being hungry. Izzie teases her by saying she should have ordered pizza before Casey confesses to not liking the pizza, describing its taste as 'a stale cracker with ketchup on it'. She explains that she's spoiled due to having a great pizza place near where she lives. Izzie suggests they go there on Friday with the team and Nate agrees leaving no room for Casey to disagree. Later on, when Casey is hanging out with Evan and mentions the meet up, he asks if he can go to which Casey agrees to.
Izzie and Casey are seen laughing and joking with the team when Evan arrives. Izzie asks if Evan is her boyfriend when he arrives as Casey jumps up before introducing Evan to everyone. They all talk about how Izzie was mean to her when they first met and how Nate was Casey's first friend at Clayton, which Evan didn't know about causing tension between the couple.
Izzie turns up at Casey's house upset after an incident with her mother's boyfriend throwing things around the house. Casey immediately hugs her in comfort. Izzie explains what happened with her mother's boyfriend, stating she told him to leave before taking the kids out of there and taking them to her grandmother's house. Casey insists Izzie stays at her house after finding out there isn't a lot of room at her grandma's place. Not long after, Sam walks through the door, where Casey introduces Izzie before they follow Sam up the stairs. When Sam feels unsure about going to sleep at Zahid's house without Edison there, Izzie suggests he take his food and leave Edison, where he is comfortable making Sam feel at ease about leaving for the night. Casey is seen smiling afterwards.
In the living room, Casey is reading a Stephen King novel to take Izzie's mind off everything, which they put down as it becomes too scary. Izzie expresses her gratitude to Casey for building the fort with Casey even offering to stay in it forever. Izzie admits that Casey is her favorite person with Casey, saying it back in return, but tells Izzie she can't tell Sharice in a joking manner.
Later on, there is a knock on the door, which Casey jokes about it being 'Pennywise'. Izzie confesses to texting Nate, which is why he turned up and suggests watching a movie. Casey turns around to say she will fall asleep, which is shown to be right as she is seen sleeping when Nate has been let in. As Nate and Casey talk and she thanks him for being her first friend at Clayton Prep, he leans in kissing her. Casey pushes him away instantly, stating they will never happen and kicks him out. Casey is later seen laying in bed next to Izzie wide awake as she sleeps.
After the incident with Nate last episode, Casey writes Izzie a note due to being too scared to tell her what happened in person. Just as she's trying to put the note in her locker, Izzie walks around the corner, joking about it being a love note for her. Casey tries to hide the note, but Izzie pries it from her fingers reading it in front of her with Casey stating she wanted to tell her in person but chickened out. With Izzie's mixed emotions, Casey offers to go somewhere to talk about it which Izzie declines saying she needs time to think before walking away.
Casey is seen talking to Evan about it in her room. In reference to Izzie, she says, 'I like love her. We got so close so fast', before continuing to say she and Izzie are so alike with a hope of them being alright again. This is the first time Casey has expressed how much she cares about Izzie. It is unclear at this point if she references her friendship or her possible feelings. However, you can see the evident worry on her face about them not talking.
The next day, Casey tries talking to Izzie, who brushes her off and reveals she hasn't broken up with Nate, but is in fact taking his side, since he twisted the story, stating Casey kissed him instead. Izzie admits she doesn't know what to believe. Casey tries to get Izzie to believe her, but she tells Casey to back off, even using her real name instead of her nickname 'Newton', before walking away with Nate. This is the first and only time Izzie calls her this. After hearing Nate twisted the story, she storms off down the hallway in the opposite direction.
Casey mentions Izzie at the start of the episode, when she is seen getting Evan to try dipping cheese in apple juice. He teases Casey about her missing her friends which she first denies, but then admits 'Izzie would have loved this though.' Later, Casey is seen getting ready in the locker room, but when she gets her trainers out the locker, they have the words 'Slut' and 'Hoe' on the toes. Casey tries to rub it off with a paper towel and water, but it doesn't work. She is seen emotionally distressed by this. It is unclear whether the track team did this or Izzie herself. When Elsa finds out what happened, she buys her a new pair.
It's Casey's birthday in this episode and she and Izzie are still not talking. When Doug is teaching Casey how to drive, it's mentioned that Casey doesn't have any friends, so she has more time for her studies, implying neither the track team nor Nate are talking to her. When Doug asks about Izzie, Casey looks upset before telling him they aren't friends anymore.
As the party is underway, Casey is shown having a good time dancing with her friends. Sam returns to play 'Ickle Bickle Beanstalk' which Casey reluctantly plays to please him. As Evan hides it, Casey does the 'Swish Boom' dance with Sam when Izzie and the track team walk in. This upsets Casey who goes into the kitchen to ask who invited them, considering they aren't talking, which Elsa admits to. Casey gets angry calling Elsa out about inviting Izzie and the team without consulting her and throwing her a party when she only wanted something small. When Evan calls her a brat for her attitude, she leaves to go upstairs. Sam stops her talking about the game they are supposed to be playing, which causes Casey to snap at him, telling him to leave her alone in front of everyone, showing anger at everything being about him, including her birthday. She shares a look with Izzie who looks upset before storming upstairs.
Casey is in her room blowing a party horn when there is a knock at her bedroom door. Shouting at Evan and her mom to leave her alone, Izzie opens the door, asking if she can come in. Casey allows her to enter her bedroom. Izzie mentions Sam getting 'jazzed up' as he found the Ickle Bickle before she begins to apologize for everything that happened, admitting she got jealous and was scared of losing someone she loves. Casey assumes she means her boyfriend, Nate, assuring Izzie she wouldn't come between them. It is unclear whether Izzie and Nate have broken up or are still together at this point. When Izzie admits she meant Casey, she explains how she felt out of place before Casey started Clayton Prep and feels like she can finally be herself, which she can't be with Nate as they are so different. This could be a reference to her sexuality or that she feels more comfortable around Casey than the rest of them, considering neither of them are as wealthy as the other students. After Izzie admits to missing Casey when they were fighting, Casey admits to feeling the same. They forehead promise with each other at Izzie's suggestion, which leads to them almost kissing, prior to being interrupted by Elsa. This is the first time Casey and Izzie's feelings for each other are shown as more than platonic.
As they go downstairs, Casey kisses Evan on the stairs in front of Izzie after apologizing to him for earlier. Izzie is shown to be visibly upset by this before walking away. When they are singing to Casey, Izzie starts off standing beside her looking happy before Sharice moves to stand between them, causing Izzie to be disappointed. When Casey is blowing out the candles on her cake; however, she is shown grinning again as she watches.
After almost kissing each other, Casey seems to be avoiding Izzie at the start of the episode as she lies about spending time with her family to spend time with Evan. She even continues to lie when Izzie texts her again, asking how it's going. Later on, when Casey is inside of her car, going to Sam's graduation, Izzie sends a picture of the both of them, prompting Casey to ask Izzie to hang out later.
- Casey and Izzie both have responsibilities to their siblings. Izzie looks after her three siblings at home because of her mom's issues, and Casey looks out for Sam constantly because of his autism.
- They are both athletic and strong runners.
- They are each other's favorite person.
- Izzie is the first person shown that Casey has openly introduced to Sam without any doubt.
- They are the first LGBTQIA+ characters to be seen on the show, right after Elsa Gardner.
- Neither of them are like any of the other students at Clayton Prep, considering both are on a scholarship.
- They are each other's first girlfriend.