Cora is first seen outside Oona's shipwreck hideout with Sven and Sofia, who she takes an instant shine to. She then tells Oona that their mother, Queen Emmaline, wants them to go back to the Merroway Cove throne room. Queen Emmaline says that a human vessel is in the cove and Plank suggests that Emmaline remove the Floating Palace out of the Cove. Cora agrees with Plank because she thinks that humans are dangerous and that they might harm Oona and her family. When Sofia admits that she's a human and that the ship is her family's ship, Cora starts acting negatively towards Sofia despite Oona's protests on her friend's behalf, though, like her mother, she doesn't act as antagonistic toward Sofia as Plank does because of her sister's obvious affection for Sofia.
When Oona is captured by the Cedric the Sea Monster, Sofia goes back to Queen Emmaline and tells her about Oona. Cora, Plank, and Emmaline all think that Sofia is lying and that her human family has kidnapped Oona after Plank made these accusations despite the fact that there is evidence against it, like the fact that Sofia and Oona are friends and the fact that Sofia knows that such a thing would anger Emmaline to the point where she would sink the ship with her family on board. Sofia is given until sundown to get Oona back and return her to Merroway Cove. After time is up and Oona doesn't come back, the Queen and Plank go up to the surface and conjure up a storm to sink the Floating Palace. Cora asks her mother if she can come, but the Queen says that it's too dangerous and that she must stay underwater.
Ariel helps Sofia to realize that both human and merpeople care about their families and they must work together to save both. Sofia realizes that she needs Cora's help to save Oona. At first, Cora doesn't believe that Oona was taken by the Sea Monster, until Sven says that he saw it with both his eyes. Sofia says that the only way to save Oona is by working together. Cora then believes Sofia's story and goes with her to the cave where the Sea Monster was. When Sofia gets Oona's comb, she throws it overboard where Cora is waiting, then Cora raises the comb and chants "Waters rise at my command!" Then a huge wave blasts the Sea Monster out of the cove and Oona is rescued. Oona then thanks Cora for rescuing her and afterward she, Emmaline, and Plank all apologize to Sofia for their behavior.
At the very end, Amber was talking to Cora, mentioning about her seashell headband, until James does a cannonball into the water.
Cora makes a nonspeaking appearance in the end of the episode, "Cool Hand Fluke" as she watches her sister's band perform at the party in the mermaids' honor.
Like a lot of older siblings, Cora likes pushing her little sister's buttons in a way Oona doesn't find funny.