The Curious walks through an empty school hallway. The narrator questions whether anyone (including The Curious) is ever truly in control of their own actions.
Pearl has recurring dreams about the sea, and hears voices telling her to "return" to the sea. She is upset that no one wants to come to her birthday party; Danny, her popular brother, unsuccessfully tries to help her. At school, Pearl joins a marine conservation group run by a volunteer named Pui, who encourages Pearl to think that she could inspire others. When Danny finds that Pearl can hold her breath under water for longer than humanly possible, he realises she has superpowers. He suggests they research her birth parents (both kids are adopted.) Together, they find out that Pearl was found abandoned by the sea as a baby.
Pearl begins to uncover other powers including using her voice to magically influence others; soon, dozens of people want to come to her birthday party. She tries to thank Pui for helping her to become more confident, but Pui says that high school popularity is a waste of Pearl's influence. Pearl begins to spend more time with Pui, and when they visit the sea together, Pearl feels that she belongs there. However, Danny notices Pearl's behaviour changing and believes she is being brainwashed by Pui. After Pearl uses newfound telekinetic abilities to make a trash bin explode in the face of a classmate who was littering, Danny confronts her. Pearl repeats Pui's words about how humans are dirty and destroy the sea; and attacks Danny using her powers. When her parents return home unexpectedly, Pearl snaps out of it and is upset at what she's done.
Pearl goes to Pui's home, where she finds Pui floating in a tank of water. Pui explains that she and Pearl are both sirens and come from the sea. She is the voice Pearl has been hearing, and has been trying to help Pearl discover who she really is. Pui tells Pearl they must return to the depths of the sea; but Danny interrupts them, wanting to free Pearl from Pui's influence. Pui says that sirens are the natural enemy of humans and exist to destroy humanity. She tries to kill Danny, again inviting Pearl to join her. Pearl decides her place is on land with her family, and steps in to save her brother. She and Pui have a brief fight but are evenly matched. Realising that Pearl will never join her, Pui disgustedly declares Pearl is no better than a human now; and vanishes into the water.
Pearl cancels her birthday party and decides to spend the day with her family, feeling that she's done with trying to be someone she's not. A year later, she celebrates another birthday, for which her parents have re-decorated her room with a tank for her to sleep in. Meanwhile The Curious takes a piece of seaweed by the shore where Pui had brought Pearl.
This episode contains examples of:
- Call to Adventure: Referenced in the episode's title, although subverted in that what Pui actually planned was for Pearl to join her in killing humans and wrecking ships.
- Refusal of the Call: Pearl's ultimate decision.
- Doorstop Baby: Pearl was found abandoned by the seashore.
- Elemental Powers: Pearl has several water-themed abilities.
- Enthralling Siren: What Pearl and Pui apparently are.
- Evil Mentor: Pui for Pearl.
- Genre Savvy: Danny comments that Pearl's situation makes her a perfect candidate for a superhero origin story.
- Granola Girl: The persona Pui adopts at the conservation group.
- Happily Adopted: Pearl and Danny.
- The Hero's Birthday: Pearl's powers come to light around the time of her fifteenth birthday.
- I Just Want to Have Friends: Pearl.
- Insistent Terminology: Pui wants to be very clear that she and Pearl are not mermaids.
- Ocean Awe: Pearl experiences this when Pui takes her to the seashore.
- Shout-Out: Danny sarcastically asks whether Pui expects Pearl to live with 'a bunch of singing crabs'
- Sibling Yin-Yang: Quiet, reserved Pearl vs brash, popular Danny.