Sofia and Miranda are riding in the Royal Coach to Dunwiddie Village. They arrive at the shoe shop that used to be their home before they moved into the castle. Inside, Miranda suprises Sofia with a lovely pink dress and matching shoes she made for her graduation from Royal Prep. Sofia loves it and changes into her new dress. Afterwards, the pair head back to Enchancia Castle. Sofia cannot believe today is her last day at Royal Prep. Miranda states that she cannot believe she went to Royal Prep or that she is a Queen, noting they have come a long way, to which Sofia sighs. When Miranda asks what's wrong, Sofia explains that the other students want her to make a speech at graduation and she does not know the right thing to say is on such a big day. Miranda assures her she will do fine. Roland, Amber, and James are excited about graduation and the Royal Family heads to the coach. Just as Sofia is about to enter the coach, however, Chrysta and Skye show up and tell her she needs to go to the Mystic Isles: Azurine has spotted Prisma on the Isle of Crystals. Sofia tells Amber, who agrees to cover for her. Sofia, Skye, and Chrysta then head to the Mystic Isles.
On the way, Sofia finds it odd that Prisma would go to the Isle of Crystals since the Wicked Nine are all in the Protectors' Castle on the Isle of Protectors. Sofia quickly realizes that her sighting on the Isle of Crystal is a decoy to lure the Protectors away while she obtains the Wicked Nine. Chrysta assures Sofia that Garish was left behind to guard the Protectors' Vault, which has an unbreakable lock. Sofia reminds her that Prisma has her Neccesi-Key and might break into the Vault with it. Sofia, Skye, and Chrysta then head to the Protectors Castle where, sure enough, Prisma has broken into the Vault. Prisma then sets in motion her plan to absorb the magic of the Wicked Nine. Using their Enchantlets, Sofia and Chrysta finally stop Prisma and recapture her. Sofia even gets her Nessci-Key back. Orion and Vega arrive with the other Protectors, who take Prisma away to imprison again. Orion notes that the Locket of Vor has been destroyed and hopes Vor is destroyed too. When Sofia asks who Vor is, Orion explains to her that she is an evil sorceress who tried to use her magic ring to conquer every single Realm eons ago. The Protectors stopped her and imprisoned her Spirit inside her Locket. They then divided up her Ring and sealed them inside the Wicked Nine. Sofia wonders if that was why Prisma was seeking the Wicked Nine. Vega reminds her that Prisma just wanted all of that power for herself. However, Vega also states that if Prisma had completed the spell, Vor would have been released. Sofia heads back to the Ever Realm to attend her graduation.
At Royal Prep, everyone is wondering where Sofia is. Amber assures everyone that she is on her way. Sofia arrives on Skye and finds Desmond, who is afraid to give his speech as the valedictorian. Sofia pulls him to the stage and they give their speeches together, to everyone's joy. Back on the Mystic Isles, Twitch and Wormwood visit Prisma in her cell. Prisma is furious that she came so far just to fail. Suddenly, Vor's spirit appears before Prisma. It turns out that she did complete the spell and freed Vor. She hands Prisma her Ring. The second she puts it on, Vor enters Prisma and becomes flesh and blood again, taking Prisma's body as her own. Vor reveals that she was using Prisma to get what she needed to resurrect herself. Now that she is restored, she now plans to get her revenge on the Protectors and Sofia. Wormwood and Twitch pledge themselves to her. Vor turns Twitch into a black unicorn and flies to the Protectors' castle. Revealing herself, Vor then imprisons the Protectors.
Back at Royal Prep, everyone is preparing to go home. Vivian is sad since they will be going to different schools. Amber tells her they will all still be friends. Everyone then leaves to go to the party. Clover comes up to congratulate Sofia, when all the sudden she gets a call from Chrysta. She informs her of Vor's release and the imprisonment of the Protectors. Sofia asks Amber to cover for her again and then heads to the Mystic Isles with Clover on Skye.
On the Mystic Isles, it is revealed that Vor has Chrysta under a mind control spell and her call was to lure Sofia into a trap. Vor plans to conquer the Ever Realm starting with the Kingdom of Enchancia. Sofia, Clover, and Skye arrive at the Protectors' Castle. Orion and the other Protectors warn her about Vor's trap. Sofia and Clover stop in time, but Skye falls into the trap: a magical glowing barrier that keeps anything from getting out of it. Chrysta reveals the real purpose of her call earlier. Vega tells Sofia that Vor's goal is to spread evil everywhere she goes and is heading for Enchancia. Orion also warns her that Vor's going to seal the gate to the Mystic Isles and if she does not get through in time, she will be trapped in the Isles forever. With Skye trapped, Sofia turns herself into a Flying Unicorn and heads to the gate. Sure enough, Vor has cast a spell to seal the gates. Thanks to her Flying Unicorn form, Sofia gets through just in time. Sofia and Clover also find Vor just in time to see her conjure a legion of Crystal Soldiers. Sofia and Clover feel they cannot handle this on their own and fly off to go get more help.
At Enchancia Castle, Baileywick and Cedric are getting the castle ready for the party. Miranda notices that Sofia is missing, only for Amber to state that she is running an errand. In return, James remarks that Sofia has been running a lot of errands lately. Meanwhile, Vivian, Desmond, Ruby, and Jade are on their way to the party at Enchancia Castle, when all of a sudden the quartet spots a pink unicorn. The unicorn is revealed to be Sofia when she changes back into herself, to everyone's shock. They ask her how she did that to which Sofia reveals the truth about her Amulet. She then tells them about Vor. The quartet agrees to help Sofia as she is always been there for them. In Dunwiddie Village, the group unleashes an ambush on Vor and her minions. Vor overpowers them with her magic. Lucinda shows up to help, but Vor is still too powerful. Sofia urges her friends to go to the castle and warn her family. However, her friends insist her to do that as they still want to help. Unfortunately, after Sofia leaves, Vor easily subdues them with her mind control spell, forcing them to tell her where Sofia is going.
On her way back to the castle, Sofia tries to summon Minimus, when Vor appears right in front of her. Sofia uses her Enchantlet to lasso Vor's wrist, but Vor snaps the rope, causing Sofia to lose her balance and fall off the bridge. Luckily, Minimus arrives, catches Sofia on his back, and flies her to safety. They try to sneak into the castle to warn her family, but Vor begins placing her powerful curse over it. Seeing how badly they are outmatched, Minimus tells Sofia he knows a perfect place to hide, and the two make a hasty retreat. Watching the heroes fly into the distance, Wormwood volunteers to go after them, but Vor states it will not be necessary, as she intends for Sofia to hopelessly watch as she takes away everything she owns and loves. Inside the castle, Vor and her army of Crystal Soldiers burst into the ballroom. Cedric tries to fight back, but Wormwood takes his wand, enabling Vor to take him and the Royal Family prisoners after ensnaring them in her mind control spell. She even forces King Roland to take his crown off for Vor to burn to signify the end of Roland's reign.
Meanwhile, Sofia and Minimus have retreated to the Secret Library. Sofia discovers Vor's conquest in the distance and feels like all hope is lost. Suddenly, her Amulet glows blue. A book called The Tale of Princess Sofia is selected. The book goes through the pendulum and the Narrator tells Sofia her latest story:
- Once, there was a young girl named Sofia. She lived in the village with her mother, Miranda, and was happy, but missed her father, a sailor, who had been lost at sea. In the nearby castle lived King Roland II, who had wanted a family so badly he tried making a wish in a wishing well. The wish came true and twins were born. But the Queen fell gravely ill. The children were happy, but never knew what it was like to have a mother. Until one day, King Roland and Miranda fell in love and married. Sofia treasured her new family more than anything and she also became a Princess with the responsibility to protect her family, friends, and all those who dwelt in her Kingdom. So when the day came that the evil Vor took everything Sofia held dear, the young Princess was faced with her biggest challenge yet.
Sofia sadly notes she already tried to give this story a happy ending and she failed. The Narrator reminds Sofia that she is the Storykeeper. Suddenly, the pendulum then turns into a man who is revealed to be the narrator--the first Storykeeper. He explains that he built the Secret Library centuries ago and filled it with many books that remained unfinished. Sofia is one of the few who has been able to follow in his footsteps so magnificently. The Narrator then reminds Sofia that all she loves is in danger and only she can save them. However, he also explains that she must be willing to face this evil on her own and be willing to make the ultimate sacrifice. Sofia sends Minimus to the harbor to wait for her and exits the Library to save her family.
Reaching the castle, Sofia uses several clever methods to sneak inside without getting caught. First, she turns herself into a mermaid to swim back to the passageway in her room. She then enters her room with her shrinking ability. After that, she uses the Whichway Bow to find her family in Cedric's tower. Robin and Mia show up. After explaining what is going on, Sofia turns into a bird. After sending her bird friends to get help, Sofia flies into Cedric's tower. She manages to break the spell Vor cast on her family and friends, and breaks them out. When they get to the harbor, they board one of the Royal Yachts to escape. Roland intends to get his family to safety before returning to retake the kingdom, but Sofia tells her father she must stay, stating that "family" is not just those related to him, but also the entire kingdom. Roland agrees, but he still refuses to turn back because of the huge danger Vor possesses. But Amber sticks up for her sister, stating she is willing to protect her future subjects from any threat. Sofia turns into a Flying Horse and Amber rides her back to the castle.
When they arrive back at the castle, Sofia and Amber, after remembering how Elena was trapped inside the Amulet of Avalor, decide to trap Vor inside it as well. Sofia activates the ability, but Vor snatches her by the ankle, intent on dragging her inside with her. Amber grabs Sofia's hand to save her, but the force is too strong. The two sisters' hands break apart, and Sofia is sucked into the Amulet with Vor. However, with Vor trapped inside the Amulet, the effects of her magic get undone; the cursed barrier imprisoning the Protectors disappears and the people of the castle and the village are freed from the mind control spell. Cedric arrives with the rest of the Royal Family and subdues Twitch and Wormwood. Roland, Miranda, James, Grand Mum, and Tilly ask where Sofia is. Amber sombrely tells them that she is trapped in the Amulet with Vor.
Inside the Amulet, Vor quickly gains the upper hand on Sofia and prepares to finish her off. But Sofia stands tall after seeing the spirits of the Disney Princesses who had been summoned in her times of need. They encourage her to be brave and strong for they believe in her. With their support, Sofia lets the bright light of goodness in her heart shine on Vor, causing the evil sorceress to dissolve into nothingness, destroying her permanently and freeing Prisma from her control. Truly grateful and guilt-ridden for what happened, Prisma apologizes to Sofia for everything she has done.
Sofia's friends, the Three Good Fairies, and the Protectors arrive at the castle. When Amber reveals what has happened, Cedric summons his parents and, with everyone's help, casts a spell that frees Sofia and Prisma, who surrenders willingly to the Protectors. A relieved Miranda hugs her daughter. Orion declares Sofia an official Protector of the Ever Realm, and he and the other Protectors award Sofia her new Protector uniform. Cedric gives Sofia back her Amulet. Roland thanks Cedric for his help in saving his step-daughter and tells him that, from now on, he will be called "Cedric the Great". As everyone else goes inside for the graduation party, Sofia and Amber embrace each other. Sofia tells Amber that she will make a great queen, dubbing her "Amber the First". The two sisters then go inside to join the celebration.
- Ariel Winter as Princess Sofia
- Darcy Rose Byrnes as Princess Amber
- Wayne Brady as Clover
- Travis Willingham as King Roland II
- Sara Ramirez as Queen Miranda
- Nicolas Cantu as Prince James
- Tim Gunn as Baileywick
- Eric Stonestreet as Minimus
- Jess Harnell as Cedric the Sorcerer
- Jurnee Smollett-Bell as Chrysta
- Paty Lombard as Vor
- Megan Hilty as Prisma
- Andrew Rannells as Skye
- Colin Salmon as Orion
- Ming-Na Wen as Vega
- Jeff Bennett as Twitch
- Jim Cummings as Wormwood, Goodwyn the Great
- Meghan Strange as Robin
- Ashley Eckstein as Mia
- Isabella Acres as Jade
- Diamond White as Ruby Hanshaw
- Merit Leighton as Lucinda
- Sabrina Carpenter as Princess Vivian
- Harley Graham as Princess Clio
- David Sobolov as Garish
- Aden Schwartz as Prince Desmond
- Bonnie Hunt as Aunt Tilly
- Russi Taylor as Fauna, Winifred the Wise
- Barbara Dirickson as Flora
- Tress MacNeille as Merryweather
- Hugh Bonneville as The First Storykeeper
- Ellie Kemper as Crackle
- Vor wears pants during some shots on the cotton's field.
- Crackle's ears are missing after Sofia turns from flying horse to human.
- Lucinda's cape and hat turn to white during Dunwiddie's battle.
- Sofia's hands go through Cedric when they met at the last time.
- Vivian has a pink shadow when she walks to the Enchancia castle, at the end of the film.
- When Sofia and her mother are arriving near the Castle she wears the crown who Cedric later gives her for her graduation
- This is the sixth and final special in the series, following Once Upon a Princess, "The Floating Palace", "The Curse of Princess Ivy", Elena and the Secret of Avalor, and "The Mystic Isles".
- The Secret Library makes its seventh and final appearance in this special.
- Sofia's friends and family finally learn the entire truth of Sofia's Amulet.
- Tilly reveals that she knows about the Mystic Isles and the Protectors.
- During the narration of Sofia's tale, King Roland's first wish to the Wishing Well was revealed that he wanted a family, and his late queen makes a brief appearance. Sofia's birth father is also mentioned as well.
- Inside the amulet, several symbols associated with the princesses pass by Sofia: the Magic Mirror (Snow White), a crown (Aurora), a golden rose (Belle), the Pumpkin Coach (Cinderella), a frog (Tiana), a dragon (Fa Mulan), a lamp silhouette (Jasmine), the Clan DunBroch emblem and bear prints (Merida), autumn leaves (Pocahontas), the golden sun and hair (Rapunzel), a snowflake (Elsa and Anna), and the Scepter of Light (Princess Elena).
- This is the first and so far, the only episode not to feature a title card.
- This is the second and final episode/special to have five songs, the first being the pilot Once Upon a Princess.
- Grand Mum appears in the finale, but has no lines due to Florence Henderson's death of a heart attack back in November 2016.
- Moral: The people you love and who count on you are worth any risk or sacrifice on your part.