The episode begins with Bingo excitedly running towards her parents, holding a swimming cap and announcing that she’s learned to swim and doesn’t need floaties anymore. Bandit tells her to walk, not run, near the pool, and Bingo apologizes. Bluey then runs into the scene, eager to play a game called Swim School, and Bingo tells her parents that Bluey was running near the pool. Bandit scolds Bingo for being a dobber, but she’s confused because he just told her that running near the pool is dangerous.
As Chilli applies sunscreen to the kids, Bandit tries to explain the rules, but gets tongue-tied and asks Chilli for help. She shrugs, and he decides to roll into the pool instead. The title card appears, and then the scene cuts to Bluey explaining the rules of Swim School to Bingo and Bandit. They learn about the two classes: Little Fish and Big Fish. Chilli joins in, and they all meet their teacher, Karen, who introduces herself and explains that they need to pass Little Fish before moving on to Big Fish.
Karen starts the Kicking class, and Bingo shows off her kicking skills. She corrects Karen when she gets her name wrong, saying it’s actually Merifyndor. Bandit sings while kicking, but gets a bit off track, and Chilli points out that he’s not doing it properly. Karen tells Chilli not to be a dobber, and Merifyndor pokes Bandit in the belly, prompting Karen to remind her to keep her hands to herself. The Kicking class ends, and Karen establishes two new rules: no poking and no dobbing, unless someone’s in danger.
The doggy paddle class begins, and the kids compliment each other on their swimming. Karen is impressed and tells them they’ll be Big Fish in no time. The lesson moves on to monkeying, and then ninja kicks. Karen demonstrates a ninja kick, and the kids are all impressed. They try it out, and Karen congratulates them on passing Little Fish. Merifyndor notes that no one dobbed on anyone, and Karen wishes them good luck before swimming off.
The kids meet their new teacher, Margaret, who welcomes them to Big Fish. She’s strict and warns them that if anyone steps out of line, they’ll get a squirty. Margaret tells them that dobbing is good, and if they don’t dob, they won’t pass. The kids are confused, having learned that dobbing is bad in Little Fish. Margaret puts them through a series of challenges, but they all end up failing. Bevan makes fun of Margaret, calling her Marge, and she gives him a squirty.
The kids have a family meeting and decide to refuse to do what Margaret says. Merifyndor dobs on her siblings, telling Margaret that they don’t want to follow her rules. Margaret gives them squirties, and Merifyndor passes Big Fish. However, Sharon dobs on Merifyndor for calling Margaret a silly old watermelon head, and Merifyndor fails. Bevan tries to lie his way to passing, but ends up failing when he admits to peeing in the pool.
In the end, Merifyndor and Sharon decide to fail Big Fish too, and they all jump into the pool. Margaret tells them they’ve all failed, and then jumps in after them. Karen surprises the family by welcoming them back to Little Fish, and they all hug. Karen says she’s proud of them, and Merifyndor asks why the water is warmer. The family quickly swims away from Bevan, who had peed in the pool.
