The Royal Family of Avalor, the Turners, Mateo, and Gabe on their way by a boat under the command of Scarlett Turner to Nueva Vista to visit Elena and Isabel's paternal first cousin Duke Cristóbal. On the way, Elena is practicing the use of the Scepter of Light's powers. Gabe is amazed and asks how many powers the Scepter has. At Mateo's urging, Elena reveals a new power: Making objects invisible. However, Elena reveals she's having trouble making herself vanish with it but she can use it perfectly on objects. Suddenly, Scarlet spots some Sirenas off in the distance and tells Daniel to ready the crossbows. When Elena asks why, Naomi tells her "Sirenas are dangerous! Everyone knows that!" Naomi's parents elaborate: They sing a siren song to put sailors in a trance and makes them crash their ships. Elena and Mateo both protest that they are about to launch an unprovoked attack. Daniel and Scarlet ignore them and open fire. Elena stops them with her Scepter. Marisa, the female Sirena, sees this and stops her brother Marzel, the male Sirena, from retaliating. Meanwhile, Naomi asks Elena why she stopped the attack and Elena reiterates that it was unprovoked. Under the sea, Marzel is furious that they were attacked despite the fact that Sirenas have not sunk a ship since before they were born. Marisa states that is because the humans don't know they have changed. She then decides to go talk to their father so she can speak to Elena.
Meanwhile, Elena's group arrives at Nueva Vista to the sound of welcome bells. In the distance, Shuriki and Fiero hear the bells and know that Elena has arrived. Shuriki vows to make this a summer vacation that Elena will never forget as she has mastered the Scepter of Night. Back in Nueva Vista, Elena's group is greeted by Duke Cristóbal. Elena notes how much her cousin has aged since she last saw him to which Duke Cristóbal tells her that he did not spend forty-one years in a magical Amulet. He also tells her that he invited her to celebrate her victory over Shuriki. Elena reveals that Shuriki is alive and more powerful than ever. Duke Cristóbal assures Elena that she is more powerful than ever too and has her family to support her too.
Meanwhile under the sea, Marzel and Marsia arrive in the Sirenas Palace where the meet their parents King Pescoro and Queen Camila. Pescoro confronts Marisa about how she was spotted near a human ship. Marisa confirms this and tells her father that she thinks it is time they tell the humans that they have changed. Pescoro tells her he knows her heart is in the right place but the humans despise them for a good reason. Camilla agrees with him and tells her to stay away from the humans. Marisa goes to talk to Elena anyway with Marzel and Coco going after her.
Back in Duke Cristóbal's Palace, Esteban tells Duke Cristóbal about their run in with the Sirenas. Duke Cristóbal asks if the Sirenas attacked them. Naomi states "They were about to." to which Elena tells her "We don't know that." Elena also states that the Sirenas were never a problem when she came over to see her cousin before. Duke Cristóbal tells her that is because she was protected from the truth by King Raul, who lost his younger brother, Duke Cristóbal's father, to a Sirena attack. Elsewhere, Migs, Luna, and Skylar are flying through the jungle and discover that Shuriki is already there in Nueva Vista. They fly back and tell Elena's group. They split up to look for Shuriki. During the search, Elena hears a song and falls into a trance. She heads to the riverfront where it is revealed that Marisa is the one singing the song. After snapping out of the trance, Elena is instantly fearful of the Sirenas. Marisa tells her not to be scared as she and Marzel just want to talk to her. After they give themselves legs, Marisa tells Elena that while all the terrible things she has heard about Sirenas are true they are not the whole story: They used to sink ships because they felt the need to defend their territory. However, one day after sinking a ship their father saved their mother by turning her into a Sirena. Pescoro fell in love with her. After marrying her, he ordered the attacks to stop. Marisa now wants to make peace with the humans. Elena is unsure at first due to what happened to her paternal uncle but agrees to talk to Duke Cristóbal because she believes them. Elena brings Duke Cristóbal to meet them. However, Duke Cristóbal orders his Guards to seize them. Elena stops them and the Sirenas escape. Elena asks her cousin why he did that as they came to discuss peace. Duke Cristóbal tells her that was a lie and reminds her of his father. Underwater, Marzel thinks Elena set them up. When Marisa tries to defend her Marzel snaps "Grow Up Marisa! The humans hate our kind and they always will!" That night, Elena feels guilty for Duke Cristóbal's attack.
The next day, Elena's group is taking part in a water parade. When Victor and Carla are spotted in the crowd, Mateo, Gabe, and Naomi take off on Migs, Luna, and Skylar. Duke Cristóbal makes his cannons fire confetti. Suddenly, Elena's boat goes into a side way where she finds Shuriki and Fiero, revealing that Victor and Carla were decoys to lure Elena's friends away. Elena tries to make herself invisible, but a necklace Duke Cristóbal gave her earlier enables Shuriki to see her and blast her into the water. Marisa finds Elena and wraps some milagras around her chest so she can breath underwater without getting turned into a Sirena. It works and Elena is saved. Marisa and Marzel then take her to their father for help against Shuriki. Pescora refuses and tells them about how after the attacks stopped humans thought they were kidnapping Marisa after she used her ability to turn her tail into legs for the first time. He also states that this convinced him that humans will always hate Sirenas for the attacks on their ships and forbade all contacts with humans. Elena tells him now's their chance to show humans those days are over. Marisa agrees and goes with her.
Back at Duke Cristóbal's Palace, the Royal Family of Avalor has arrived back after enjoying the parade. Suddenly, they get ambushed by Shuriki's group, who takes them prisoner. Elsewhere, Duke Cristóbal and his Guards have found Elena's float. Duke Cristóbal picks up Elena's Scepter just as she and Marisa arrive. Elena tells her cousin that Shuriki ambushed her and she will take care of her. However, Duke Cristóbal throws the Scepter into the water and has his Guards seize her. Elena asks her cousin what is the meaning of this. Duke Cristóbal explains that when Shuriki took over forty-three years ago, she gave him gold in exchange for his loyalty. After Elena defeated Shuriki two years ago, he lost his gold supply. Shuriki offered to renew it if he helped her revealing that Duke Cristóbal has been in on her trap from the beginning. Elena is shocked that her cousin betrayed his family and country for gold. Marsia tries to save Elena but Duke Cristóbal has his Guards seize her too. Marzel witnesses this and goes to tell his father. On the way, Elena informs Naomi and Luna about Duke Cristóbal's betrayal. Duke Cristóbal has Elena and Marisa thrown in a prison cell. Naomi informs Mateo and Gabe about Duke Cristóbal's treachery and they fly to the rescue. Meanwhile, Duke Cristóbal informs Shuriki that Elena is still alive but has been captured. Infuriated, Shuriki heads to the tower to finish the job. Meanwhile, Naomi's group arrives and busts the Royal Family and Marisa out.
Shuriki's group pursues them. The Sirenas show up and help by making Duke Cristóbal's ship crash. Marzel tosses the Scepter of Light to Elena, who begins a clash of the Scepters with Shuriki. Meanwhile, Mateo fights Fiero and soon overpowers him. Fiero takes Gabe hostage so he can use him as a shield. Naomi frees Gabe and Mateo turns Fiero to stone again. Shuriki tries to kill Elena, only to miss thanks to Elena's Invisibility Power saving her at the last second. Elena hits Shuriki with Blaze at point blank range, killing her for good. The Delgados escape on Cruz and Vestia with the jewel of the Scepter of Night. Duke Cristóbal is arrested and is ordered to be incarcerated. When Duke Cristóbal protests that they are family, Elena walks up and retorts "You don't even know what that word means." Elena then declares the Sirenas friends of the Avalorans.
- Aimee Carrero as Princess Elena
- Jenna Ortega as Princess Isabel
- Emiliano Díez as Francisco
- Julia Vera as Luisa
- Christian Lanz as Chancellor Esteban
- Jillian Rose Reed as Naomi Turner
- Joseph Haro as Mateo
- Jorge Diaz as Gabe
- Rich Sommer as Daniel Turner
- Julie Nathanson as Scarlett Turner
- Jane Fonda as Shuriki
- Myrna Velasco as Carla Delgado
- Lou Diamond Phillips as Victor Delgado
- Héctor Elizondo as Fiero
- Carlos Alazraqui as Skylar
- Chris Parnell as Migs
- Yvette Nicole Brown as Luna
- Gina Rodriguez as Princess Marisa
- Prince Royce as Prince Marzel
- Travis Willingham as Cuco
- Edward James Olmos as King Pescoro
- Javier Muñoz as Duke Cristóbal
- Rita Moreno as Queen Camila
- Rosario Dawson as Daria
- Rich Horvitz as Ocho
- Mario Lopez as Cruz
- Diane Guerrero as Vestia
- Gia Lopez as Young Marisa
- This is the last episode to premiere on Disney Junior before returning to Disney Channel.
- Shuriki is finally killed off in this episode and Fiero is turned back to stone.