Mia and Sara are woken up by Sara's mother, who brings them breakfast. The girls promise to look after the animals and to have dinner ready by the time Sara's mother returns home from work. Sara touches Mia's bracelet, expressing curiousity about it. Mia explains how it was a present from her parents, who died when she was twelve. Sara apologizes for bringing it up, but Mia says it's fine. Sara shows Mia around as they bring food to the animals. Eventually, Mia's bracelet begins to glow, and Mia excuses herself by claiming she needs to use the bathroom. While Mia tries to find her book, Sara ends up having to go to the bathroom as well, and is confused to hear Mia moving about in a different room searching for her things.
Mia manages to find her book, and travels to Centopia. Mia heads to the castle to help investigate the crystal. Mo and Yuko are discussing how Phuddle claimed the Pan King had a similar crystal. Mia tells them about the riddle, but are confused that the riddle warns about a king in a bad mood, since the Pan King is usually in good spirits. However, when they go to meet the Pan King, he believes them to have stolen the pink crystal from him. Mia tries to explain that they believe his crystal is a different one, but the Pan King insists there's only one. Mia assures the Pan King that they'll figure things out, as Mo and the Pan King depart on bad terms.
Lord Drakon is giving Gargona and Dax new orders. Gargona tells Dax to find out where the winged unicorns are, and Dax calls on his bug minions, telling them to spread out and gather information.
Mia, Yuko and Mo come across Phuddle while Mo is still annoyed at the Pan King's accusation. Phuddle claims that pans have a habit of hiding things and forgetting about where they hid them, suggesting the same may be the case with the Pan King. Mia recalls the riddle, and Phuddle suggests the place mentioned in the riddle must refer to Bolobo Mountain. The elves go to investigate, while in the meantime, the Pan King and his wife get into an argument over whether the Pan King forgot his remembering rule for his hiding place. The elves spot the Pan King heading to Bolobo Mountain to look for the crystal as well.
When the Pan King notices the elves, he accuses them of having followed him. Mo and the Pan King continue to argue, but Mia says the whole thing is just a misunderstanding. When the Pan King gets stuck in a hole, Mo tries to help him out. However, in the process of helping him, part of the cave starts to break apart, trapping Mo and the Pan King and locking Mia, Yuko and Onchao out of the cave when the entrance caves in. Onchao tells Mia and Yuko to trust his instincts as they go to look for another way back in.
Mo's right leg is injured, as is the Pan King's right hand. As Mia and the others manage to find another way back into the cave, Mo apologizes to the Pan King for insulting him earlier, explaining his worries about not being able to protect the island. The Pan King admits that he probably should've been more patient as well, and being a more experienced king he should've tried to set a better example. As the two patch things up, the butterfly from Mia's friendship ring finds them. The two of them work together to find a way back to the others.
The two manage to get back to the others, and Onchao uses his tears to heal the Pan King's hand and Mo's leg. The Pan King realizes the place they are in looks familiar, and leads the group further in. The group find some murals depicting an old legend about Centopia's Heart. The Pan King explains that the continent of Centopia was once shaped like a complete unicorn, where the two unicorns who would become the ancestors of all unicorns lived. One day, one of the unicorns left to explore, promising to return, but never did. The unicorn that stayed behind was sad and lonely, and eventually, its heart broke into pieces, and along with it, the continent of Centopia broke into smaller pieces. Centopia's heart took the form of the pink crystals. The crystal Mo had begins to glow, and they find the fragment the Pan King hid away.
One of the bugs that had been following the group returns to Dax and Gargona to report its findings. Dax goes to report to Lord Drakon.
The Pan King's wife shows up, telling him he was right earlier and that they both had the same remembering rule, before noticing that he found the crystal and remembered on his own. The Pan King gives Mo his shard, and Mia has to return to her own world. She promises to help them begin the search for the rest of the pieces when she returns, so they can reassemble the Heart of Centopia and save the king and queen.
When she returns to her own world, Sara asks about where Mia really went off to, and Mia admits that she does have a secret. Mia promises to tell her sometime, and Sara tells her there's no pressure, since they do have the whole summer to get to know each other better.
