Katie and Sadie were introduced to the island as Best Female Friends For Life, (BFFFL's) and were extremely alike. They met in their childhood and were inseparable friends since then. In Total Drama Island, their friendship is used many times as a gag, with things such as them doing absolutely everything together, and sometimes even syncing each other (such as in The Big Sleep, when they snore together). They sometimes reached delicate points in their friendship (such as when they were fighting over Justin or when they both argued with each other about getting lost), but most of the time they are almost naturally seen as great friends. They interact in virtually all the episodes where they are seen together, and many times share good memories from their childhoods (often through rambling), which indicates that their friendship was, in most of their lives, at the same status as it is today. The fact that Katie is tan and petite, while Sadie is pale and overweight, being the near-only major difference between the two.
In Katie's audition tape, the two of them dance together. Sadie appears concerned when Katie hits the camera and falls over. In Sadie's tape, the two have a pillow fight, where Katie hits Sadie softly but Sadie hits Katie too hard, knocking her out. She then stops the camera.
Katie and Sadie arrive at the island together, introducing themselves as BFFFLs (Best Female Friends For Life). They are together for most of the episode and get very upset when Chris forces them into separated teams.
Sadie refuses to do the challenge unless she can do it with Katie who has been assigned to a different team. To spare Chris (and the others) the irritation, Izzy volunteers to switch teams with Katie so that the two can finally be reunited, which Chris quickly allows. Since then, both Katie and Sadie were Killer Bass members for the rest of the season. While dragging their hot tub materials back to the campgrounds, Katie and Sadie spontaneously feel the need to go to the bathroom at the same time. Since there is no actual bathroom in sight, Katie and Sadie squat in the forest to do their business, but they unknowingly do so on poison ivy, which leaves both of them itchy and nearly incapacitated for the rest of the challenge since all they can do is scratch themselves.
Katie and Sadie fall asleep roughly at the same time. They follow a distinct pattern while sleeping together: One will inhale while the other snores, and the pattern continues between the two. This is noted by Trent, who observes them and comments on their synchronization.
In an attempt to enter the talent contest, Katie and Sadie do a dance routine (similar to the one they both performed in their audition tapes), but the rest of their team is appalled by it, and they do not qualify to perform in the show.
While traveling with their team into the woods, Katie comes across a blueberry bush and the two stop to eat their fill of blueberries. Sadie realizes that the team did not notice their stopping, and therefore were separated from the duo. While looking for their team, Katie and Sadie reminisce of the misadventures they had together since they were small children, and even incidents between the two that happened as recently as the past year. Eventually, the two begin to start to argue, with Sadie throwing the first stone by blaming Katie due to her poor sense of direction. Katie then retaliates by making fun of Sadie for not having a drivers license unlike herself, but Sadie points out that her lack of a sense of direction has caused Katie to crash cars into buildings. Differences between the two are made apparent in this scene. One topic after another, they finally dig deep enough into each others' skin to announce that by the time they return to camp that their BFFFL status would be over. Unable to find their team, the two take refuge in a cave. As darkness, rain and fear envelopes them, the two huddle each other, hoping to live through the night.
The next morning, Katie and Sadie wake up to find a bear returning to its den and chases them out of its home. The two eventually make it back to the campgrounds where both teams have returned. After everything they had been through, Katie and Sadie apologize to each other for all of the nasty things they've said to each others' faces reaffirm their sisterly love for each other, and hug. Courtney is quick to cut in and yell at them for causing the team to lose the challenge. Because of this, the two are in the bottom two during the Campfire Ceremony but it is Katie who is eliminated in the end. Sadie tries to rejects the marshmallow since she would "totally die" without Katie around. However, in a sudden moment of maturity, Katie pulls Sadie together and assures her that she is better than she think she is and wishes for Sadie to press on and do her best for both of them. As Katie is taken away on the Boat of Losers, they cry out to each other that they already miss each other. When Katie disappears into the distance, Sadie is left sobbing at the Dock of Shame.
The episode picks up right where the last one left off, showing Sadie still crying at the dock. Bridgette remains by Sadie's side, trying to encourage her by saying Katie would want her to move on. She manages to take Sadie away from the dock, but Sadie's determination to stay ended up with Sadie taking off a wooden plank of the dock with her, which she clung to for the rest of the night as she continued to cry.
Over a minor grudge from Courtney, Sadie is eliminated from the competition. Sadie does not take the loss well, calling the rest of her team "marshmallow-eating freaks" before running off to the dock, sobbing. Fortunately for Sadie, she was met with a surprise when she finds Katie waiting for her on the Boat of Losers. Sadie's sadness instantly faded as she hugged her best friend and squealed happily.
Katie and Sadie are constantly together as usual at Playa Des Losers, interacting with Noah and Izzy while admiring Justin from afar. They agree with each other on many things regarding the final five campers that remain on Total Drama Island, especially gushing over Leshawna even though they were never on the same team as her. When asked who they would like to win the competition if they could make it so, Katie and Sadie misunderstand the question and vote for each other. When it was pointed out that they would have to be in the final five to get a vote, the two admit they have no idea who they would vote for. When Chris allows the eliminated contestants to choose who will join them at the resort, Katie and Sadie misunderstood him and instantly voted for Leshawna, indirectly leading to Leshawna's elimination after everyone accidentally mentions her name.
Katie and Sadie continue to admire Justin at the beginning of the episode and join him in finding the million dollar case, though Justin is only using the two of them to do the dirty work for him. However, Katie and Sadie are so enamored and distracted by his beauty that they are of little help to him. He finally abandons them at a cave, giving the excuse that he needs to use the bathroom. Not at all sensing the rejection vibes, the girls quickly agree and remain in the cave awaiting Justin's return.
To pass the time, Katie and Sadie play magic squares to find out who Justin is in love with, not realizing that he dislikes the both of them. Katie plays first, and gets the result that Justin is in love with her. Consumed with jealousy, Sadie takes the magic square and asks it who Justin is really crushing on, and the answer is then Sadie. Katie accuses Sadie of stealing Justin from her, beginning another heated argument between the two BFFFL, even bringing up past incidents. This prompts another break-up between Katie and Sadie as they leave the cave and walk off, still following each other but "not listening" to each other. Along the way, the two are chased by a moose that was also chasing Geoff and Bridgette and the four have the climb to the top of the diving board that led to a pool of green jelly from Phobia Factor. As they are climbing, Katie and Sadie make amends. One incident after another, Katie and Sadie fall into the pool and are unable to reach the Dock of Shame in time. Because of this, they were among those who were ineligible to compete for the money again in Total Drama Action.
Katie and Sadie appear with the other characters who failed to qualify (and the four who qualified but were already eliminated) in a side-show starring Geoff and Bridgette, where they commented on the happenings of Total Drama Action so far. Many characters talk about the subject of Gwen and Trent's recent break-up; while Katie and Sadie are on Trent's side (and even offer to be substitute girlfriends for Trent), Katie and Sadie veer off the topic and feud for a third time over the topic of Heather tricking Trent by kissing him, which broke Gwen's heart and ultimately got Trent eliminated in Search and Do Not Destroy during the first season. After hearing Trent's story about why nine is his lucky number, they quickly made up. In the exclusive clip, Katie and Sadie stand outside of Trent's dressing room, hoping to ask him out. When Sadie brings up that only one of them can be his girlfriend, the two end up fighting again.
Katie and Sadie get into another fight when the two keep staring at Trent, and are often very distracted by him during the episode. They also reveal their hatred for Gwen.
In the special, both girls are seen helping Gwen with her video blog, however, they are considered an annoyance rather than assistants. When they are interviewed by Sierra, Katie and Sadie inform that they have switched from wearing pink to green. At the red carpet, both girls become nervous when informed by Sierra that about ten million people are watching them. In order to regain their popularity, they team up with everybody else to stop the Total Drama Dirtbags bus to the awards, however, they get stranded in a canyon. They (along with Beth, Eva, Justin, Trent, and DJ's mother) go with Geoff to look for help, and they seem a little disappointed when informed they would not compete in Total Drama World Tour.
The girls are sitting together in the peanut gallery with the other non-qualified contestants and are happy to be with each other. They are dancing with each other, along with Beth, while watching The Drama Brothers performing but eventually get into a slap fight with one another. They are also seen crying over Bridgette's song and are happy that Geoff and Bridgette make up, and are hugging each other as they make up.
Instead of helping to answer calls for donations, Katie and Sadie use the phones to talk to each other, earlier in the episode.
- This is the first pair in Total Drama who already knew each other prior to coming onto the show, the second being Duncan and Mike, followed by Amy and Samey.
- Both were the first pair to use the confessional together.
- In the first three seasons, Katie and Sadie fall for a different male contestant:
- Both girls, along with Blaineley and Eva, are the only first generation contestants to only compete in one season, which is Total Drama Island.
- They are the only two females from the original cast who have never made it to the merge, and two of the only five contestants from the original cast to never do so, the others being Ezekiel, Noah, and Tyler.
- They are the first pair of contestants in Total Drama history to take the elimination exit together.
- Their voice actresses, coincidentally, voiced two characters on 6teen who are also rarely seen apart from each other and greatly resemble each other.