At Royal Prep, the Princess Adventure Club is having a meeting. Princess Zooey announces that at next week's meeting they will present the Scroll of Discovery, which will note all the amazing discoveries they have made and will be placed in the trophy case for all to see. Sofia's addition to the scroll will be her discovery of an ancient idol in a temple in Tangu, Clio's addition will be her discovery of a new species of Rainbow Moth, and Amber's addition will be her discovery of Amberina Major. Princess Hildegard does not voice what her addition will be and claims it is because she has too many to pick. As Zooey leads everyone to where they will discuss their next adventure, Sofia notices that Hildy is upset. She admits that the real reason she did not voice her addition is because she has not made any discoveries. Sofia says she could make a discovery during their next adventure, and they go off to find the rest of the club.
In the Club's Adventure room, Zooey announces the Club's next adventure: Exploring the Lost Pyramids of Khaldune. Amber is confused as to how they will explore the Pyramids if they're supposed to be lost. Zooey explains that they were lost for centuries: An evil wizard named Hizzan built them centuries ago to hide his stolen treasures. They were discovered by the famous archaemagicalogist Princess Cassandra: a person who studies ancient magical objects. According to Zooey, there were five Lost Pyramids and Hizzan arranged them into a pattern. Hildegard believes that they cannot find the fifth Lost Pyramid and that they should pick a different adventure. When Hildegard puts her hand on a map with the Lost Pyramids on it, Sofia deduces and reveals Hizzan's pattern: In the shape of a hand. Using a diagram Sofia drew around Hildegard's hand, the Princess Adventure Club is able to figure out where the fifth Pyramid is. As they head to the hydrofoil, Hildegard gloats about her discovery, to which Amber and Clio look at her in disbelief. Zooey reminds Hildegard that it was Sofia who discovered the pattern, to which Sofia states that it was because of Hildegard. Hildegard thanks Sofia for giving her the credit, to which Sofia tells her it was a team effort. Disappointed, Hildegard vows to discover something big all by herself on their adventure.
Later, the Princess Adventure Club is on route to the Kingdom of Khaldune in Zooey's hydrofoil. Along the way, they receive a surprise visit by Princess Cassandra, who flies in on a gryffin. Zooey explains that she is going to be their guide. When Cassandra asks who discovered where the fifth Lost Pyramid is, Hildegard is about to say it was her, only for Sofia to step in and say it was a team effort. Cassandra tells the Club that every archaemagicalogist needs help and introduces the Club to her Guide Lemur, Sally. This makes Zooey deduce and reveal that Cassandra is blind.
The group arrives in the Kingdom of Khaldune. Cassandra leads the group down and asks them what they see. Hildegard tells her she cannot see anything other than miles of desert. She starts to think Sofia got it wrong, but Cassandra is convinced that she got it right as Hizzan was tricky. Hearing this, Hildegard vows to find the final Lost Pyramid. However sometime later, they still have not found it. Cassandra tells the club that sometimes the answer in front of them cannot be seen. Hearing this, Zooey decides to use the hydrofoil's cannon to blow the sand away. Afterwards, Hildegard spots a rock with a picture of a sphinx on it. The picture is revealed to be a switch and when Hildegard presses it the fifth Lost Pyramid rises out of the desert. Hildegard declares that she found the final Lost Pyramid, to which Clio reminds her that it was because of Zooey's idea much to Hildy's chagrin. Cassandra leads the group inside.
Inside, it is completely dark. When Hildegard asks Cassandra how they are going to see where they are going, she tells her that the Lost Pyramids all have Forever Torches on the walls. Sofia finds one, and after being told to do so by Cassandra, pulls it down, lighting the place up. They come to a wall with pictures that Cassandra notes are hieroglyphics. Zooey explains that a long time ago people used to write in pictures instead of words. Sofia asks Cassandra if they should tell her what they look like, but she says there is no need. She can feel what the hieroglyphic carved in the stone are, which is how she fell in love with archeomagicology. Using this ability, Cassandra reads the hieroglyphics and reveals that this Lost Pyramid has the greatest treasure Hizzan stole: The Oasis Stone. Cassandra explains that years ago Khaldune used to be lush and green thanks to the Oasis Stone. After Hizzan stole it and put it in the temple, he built all kinds of booby traps. Cassandra and Zooey want to find the Oasis Stone to bring life back to the desert Khaldune has become ever since it was stolen. Cassandra opens the wall and leads them in. They quickly arrive at the first trap: A pit they cannot see the way across. Cassandra tells them to close their eyes and asks them what they smell. Amber smells Hildegard's perfume, Fleur de Freezenburg. Sofia however smells moss. Cassandra sends Sally to find the moss, which they use to get across. Cassandra compliments them as they are beginning to rely on their other senses to get them through.
After a watery ride, Cassandra leaves the others behind to scout ahead. Hoping to get the Stone first, Hildegard goes after her. While they search the next room, Hildegard finds a switch with a jaguar on it, which, thanks to Cassandra's translation earlier, she knows leads to the Oasis Stone. After Cassandra leaves, she presses it and goes into a secret passageway. When Cassandra gets back with the others, Sofia uses her sense of smell to find out what Hildegard did and goes after her. She finds her just as she is about to grab the Oasis Stone. A Sphinx awakens and demands to know how she discovered the way in. Hildegard lies by saying she discovered everything all by herself. This proves to be a mistake as this makes the sphinx decide to trap her. The others show up and help Sofia rescue Hildegard, who grabs the Oasis Stone. They head back outside.
Back outside, the group finds King Nasir and his staff waiting for them. When King Nasir realized the fifth Lost Pyramid had been found he came to see who found it. Hildegard reveals that she recovered the Oasis Stone. At King Nasir's request, the group takes it to the top of the Pyramid. The Stone's magic turns the desert back into the valley it once was. King Nasir says that Hildegard has made the greatest discovery in all of Khaldune, but Hildegard says she made a greater discovery - that she has wonderful friends, crediting them all for helping in finding the stone.
- Ariel Winter as Princess Sofia
- Madison Pettis as Princess Cassandra
- Darcy Rose Byrnes as Princess Amber
- Harley Graham as Princess Clio
- Coco Grayson as Princess Hildegard
- Fiona Bishop as Princess Zooey
- Sean Schemmel as King Nasir
- Dee Dee Rescher as Sphynx
- Jamie Mitchell as Pilot
- Princess Cassandra is the first princess made by Disney to have disabilities.
- Moral: It's always important to give credit where it is due.
- "Speechless, GLOW, Chicago Med and Empire Among Dozen Shows Honored by 2018 Sentinel Awards". Hollywood, Health & Society (August 29, 2018).
- "Sofia the First wins 2018 Sentinel Award". YouTube (October 4, 2018).