At Enchancia Castle, Sofia is having a flying derby race with her friends when her Aunt Tilly suddenly arrives and pays a visit. Upon arriving at the castle, Aunt Tilly asks Sofia how she's doing with the book she gave her. Sofia tells her she is still at Chapter Twelve and comments how she never knew there were so many Kings and Queens in Enchancia. Tilly tells her niece that there is a lot of history within the walls of Enchancia Castle and reminds her to read Chapter Seventeen, which is her favorite. Sometime later, Sofia reaches Chapter Seventeen of the book and finds a little blue book called Behind the Walls, a book about secret passages in the castle, inside it. Clover comes in and, upon being told by Sofia what she is reading, shows her the passageway he uses to get inside the castle. When Sofia goes up to take a look, her Amulet suddenly glows sapphire blue. Sofia enters the passageway using her shrinking ability. After returning to normal size, Sofia goes down the tunnel using her Amulet as a guide. Her Amulet's light guides her to a crystalline boat which she gets on. The magical boat takes Sofia through a tunnel where she passes settings referencing the worlds of Disney Princesses. At the tunnel's end, the boat drops Sofia off at another staircase that leads to a gate. When Sofia notices that the keyhole looks like her book, she realizes Behind the Walls is the key and uses the blue book to open the gate and goes inside.
Sofia enters a room stocked to the brim with shelves of books. A floating elevator drops from the ceiling and Sofia gets on it. The elevator takes her all the way to the top where she sees her castle in the distance. A wowed Sofia wonders where she is. Tilly appears and tells her she is in the Secret Library, a library where most of the books do not have endings. Tilly explains how when she was a young Princess she wore the Amulet of Avalor and how the Amulet led her to the Library thirty years before. Tilly also tells her that she is the Secret Library's Storykeeper, the person whose job it is to go out and give each story in the Library a happy ending, and how she has chosen Sofia to be the new Storykeeper because the Amulet chose her and she passed all her secret tests. The Library's books begin to glow and a book floats off a shelf and lands into Sofia hands. The book is called The Tale of Wildwing Valley, which is the first story Sofia has to finish. It tells the story about Minimus' brother, Mazzimo, who wanted to live free as a wild horse in Wildwing Valley, a magically hidden land where enchanted creatures roam free. Unfortunately, Mazzimo was captured by the Knights of Borrea and taken to Borrea Castle where he has been held against his will by Prince Roderick ever since. Tilly tells Sofia that to give this story a happy ending she has to save Mazzimo and grant his wish to live in Wildwing Valley. Sofia is not sure she can do it on her own so Tilly offers to come along and help out just this once. After changing into her Storykeeper outfit, Sofia heads to the stables to get Minimus and flies off for Borrea with Tilly.
When they arrive at Borrea Castle, Sofia and Tilly split up to find Mazzimo. Sofia and Minimus sneak into the stable to find the latter's brother. Upon finding him, Minimus yells at Mazzimo for taking off and leaving their family for no reason to which his older brother states that he had a reason. Minimus continues to vent, ranting how they came to save him and that this is the nicest stable ever. Prince Roderick's other horses, Tempest and Elegra, tell Minimus that that is what they keep telling Mazzimo but he does not listen even though they have heated stalls. Annoyed, Mimimus tells them the only way to heat his stall is to have a dragon set it on fire. Mazzimo tells them that while Borrea Castle's Royal Stables is nice "a cozy cage is still a cage," and he'd rather be free. Sofia breaks it up and starts trying to get him out as Tilly arrives. Suddenly, Prince Roderick appears with his stable master Gavin. After introductions are made, Sofia tells the Prince of Borrea that Mazzimo wants to be free but Roderick refuses to listen and orders Gavin to open the stall so he can take him for a spin. As soon as the stall is open, Sofia tells Mazzimo to fly for it and she and Tilly trip up Roderick and Gavin so they and Mazzimo can get away. Not willing to lose such a fine horse as "Thundercloud", Roderick and Gavin give chase but Aunt Tilly loses them with one of the devices in her bag. However, Minimus is still angry and too busy arguing with Mazzimo that he becomes too distracted to pay attention to where he's going. This causes him to almost crash into a tree in a way that makes Sofia fall off him. Tilly catches Sofia in a way that makes them lose her bag. The two brothers are so worried about Sofia that they do not notice that Roderick and Gavin have caught up enabling them to capture the two horses. Roderick orders that they land so the two horses can be secured for the ride back to his castle. Sofia thinks they need Aunt Tilly's bag since Roderick has a sword and all they have is an umbrella, despite her aunt's assurance that the umbrella can be mightier than the sword. They both land and look for it. During the search, Sofia gives into despair and her doubts about whether she has what it takes to be the Storykeeper resurfaces. Her Amulet glows and an arrow is shot in her direction. The shooter is revealed to be Princess Merida. Sofia tells Merida about how she is looking for Tilly's bag but Merida tells her she does not need it and what she does need is the belief that she can save the day herself. Sofia continues to voice her doubts through a lament but Merida tells her that if she believes in herself and what she can do she can do anything. After shooting an arrow successfully, Sofia resolves to save the day on her own and takes off on Athena while Tilly and Merida watch proudly.
Meanwhile, Roderick and the others have landed and Minimus and Mazzimo have been secured. Minimus hates how he has been tied up and Mazzimo tells him that is how he feels every day he spends in a horse stall and why he left home despite loving his family and the two brothers reconcile. They take off for Borrea Castle. Suddenly, Sofia arrives on Athena. After sending her back for Tilly, Sofia hops on to Minimus and frees him. Gavin alerts Roderick who tells Sofia to fly along home. Sofia unseats him using Tilly's umbrella. Gavin goes after his master while Sofia frees Mazzimo. Upon doing so, they fly away with Tempest and Elegra following suit due to having enough of Roderick, leaving him and Gavin stranded. After Tilly arrives with her bag, they set off for Wildwing Valley, where they are welcomed by Marshand. Mazzimo and Minimus part on good terms and Minimus, Sofia, Athena, and Tilly head back to Enchancia. Upon arriving back in the Secret Library, Tilly congratulates Sofia for finishing her first story. When Sofia asks what is next, Tilly tells her to have a seat and find out.
- Ariel Winter as Sofia
- Bonnie Hunt as Aunt Tilly
- Eric Stonestreet as Minimus
- Ruth Connell as Merida
- Cary Elwes as Prince Roderick
- Hugh Bonneville as The Narrator
- Dean Norris as Mazzimo
- Wayne Brady as Clover
- Fred Tatasciore as Gavin
- Abigail Mavity as Tempest
- Grey DeLisle as Ellegra
- Jessica St. Clair as Athena
Home Video Release
- It is the first installment of The Secret Library story arc.
- In this episode, Merida is the first and only Pixar character to appear in the series to aid Sofia.
- Bonnie Hunt is known for her Pixar roles, and Merida was right next to Tilly in the end of the song.
- This is the fifth time Sofia and Minimus go off on a mission together. The first four times in the series were in "Finding Clover", "Princess Butterfly", "The Leafsong Festival", and "Carol of the Arrow".
- Sofia becomes the Storykeeper of The Secret Library.
- Sofia wears her Storykeeper outfit for the first time in this episode.
- Tilly is revealed to have a flying horse named Athena in this episode.
- Instead of being voiced by Kelly Macdonald, Merida is voiced by Ruth Connell who also provided her voice in the Disney INFINITY trilogy.
- Prince Roderick is the second villainous prince on the show, the first being Prince Hugo. However, unlike Roderick, Hugo reformed, making Roderick currently the only villainous prince on the show.
- Merida is the tenth and final Disney Princess to appear in the show.
- The first was Cinderella in Sofia the First: Once Upon a Princess.
- The second was Jasmine in "Two to Tangu".
- The third was Belle in "The Amulet and the Anthem".
- The fourth was Ariel in "The Floating Palace".
- The fifth was Aurora in "Holiday in Enchancia".
- The sixth was Snow White in "The Enchanted Feast".
- The seventh was Mulan in "Princesses to the Rescue!".
- The eighth was Rapunzel in "The Curse of Princess Ivy".
- The ninth was Tiana in "Winter's Gift".
- Merida is the second non-traditional animated Princess to appear on the show. The first was Rapunzel.
- Merida is the third princess to not sing after Aurora and Snow White.
- She is the first Princess to give her lesson in the instrumental bridge of the episode's song instead of singing it or just giving it.
- She is the third Princess after Jasmine and Mulan that doesn't disappear magically after aiding Sofia.
- She is the third Disney Princess not to be shown in her redesign, instead wearing her normal princess dress. The first two were Ariel and Mulan.
- She is the first princess to fire a weapon near Sofia to get her attention.
- Tilly rides a flying horse for the first time in this episode.
- Tilly meets a Disney Princess for the first time in this episode.
- While it was the first time onscreen, she probably met others before and perhaps already met Merida before since she was a previous bearer of the Amulet of Avalor.
- Cary Elwes, who voices Prince Roderick, is also known for his portrayal of Lawrence Gordon in the Saw Series, Wesley in The Princess Bride, Captain William Boone in the 1994 live-action Jungle Book, and the titular character in the Mel Brooks film Robin Hood: Men in Tights.
- It is revealed in this episode that the Amulet of Avalor has the ability to act as a compass to the Secret Library when the one wearing it has the magical book that's the Secret Library's key.
- Unlike the Amulet's other abilities, which make the amulet give off a purple glow, this ability makes the amulet glow blue.
- Sofia uses her shrinking ability for the second time in this episode.
- Tilly reveals she knows the truth of Sofia's Amulet due to being the last person who wore it before her.
- Minimus is revealed to have a brother named Mazzimo.
- This is the second episode to be narrated the first being Once Upon a Princess.
- This is the fourth episode which has a different background in the credits, the others being "Holiday in Enchancia", "Ghostly Gala" and "Winter's Gift".
- There are Disney Princess easter eggs in the secret tunnel to the library.
- The Wishing Well and the Cottage of the Seven Dwarfs from Snow White and the Seven Dwarfs.
- The Castle clock, the Pumpkin Coach and the Glass Slipper from Cinderella.
- King Stefan's Castle and the Spinning Wheel from Sleeping Beauty.
- The Blue Lagoon from The Little Mermaid.
- The Enchanted Rose from Beauty and the Beast.
- Agrabah and the Magic Carpet from Aladdin.
- The mountain, and the wind from Pocahontas.
- The lilies, the Magnolia tree and the bridge from Mulan.
- The fireflies in the log from The Princess and the Frog.
- Rapunzel's Tower, Corona castle and the floating Lanterns from Tangled.
- The Ring of Stones, and archery games from Brave.
- The snowy wind and the ice droplets from Frozen.
- This is the second time Sofia falls off Minimus, the first being Just One of the Princes.
- Tempest is Abigail Mavity's second character in the series, the first being Princess Lani of Hakalo.
- This is the fourth episode (and the second in a row) to feature only Sofia and not Amber, James, Roland, and Miranda.
- This is the first Princess episode where Sofia sings an entire song herself, instead of the princess and Sofia singing the second verse togehter.
- This is the first part of the Secret Library arc.
- Moral: "If you believe in yourself and what you can do you can do anything."
- This is the first episode where Aunt Tilly does not wear her signature outfit for the whole episode.