Fluttershy returning some Daring Do books that she borrowed from Rainbow Dash, having become another big fan of the book series. Fluttershy says she read the books all the way up to the most recently released entry, Daring Do and the Fallen Idol, but Rainbow Dash has never heard of this entry, explaining that A.K. Yearling always sends her advance copies of her books.
Fluttershy lends Rainbow her copy of The Fallen Idol, and Rainbow discovers the book was written by "Groom Q. Q. Martingale" from the villain Dr. Caballeron's point of view, portrays Daring Do in a very negative light, and even reveals that Daring Do is a real-life pony. Rainbow Dash is outraged by Martingale's libelous writing, but Fluttershy thinks the book gives valuable insight into Caballeron's perspective. Annoyed that Fluttershy is defending a known villain, Rainbow wants to warn A.K. Yearling before ponies realize she is Daring Do herself and her reputation is harmed further. Rainbow Dash and Fluttershy travel to a bookstore where A.K. Yearling is doing a book signing, and a number of readers are harshly criticizing her over the content of Martingale's book. Yearling, having wanted to share the stories of her adventures as Daring Do with the public, is miserable that Martingale is ruining her character. Coincidentally, Martingale is doing a book signing right across the street from Yearling's, and Rainbow and Fluttershy go to confront him. The two discover that "Groom Q. Q. Martingale" is Dr. Caballeron in disguise, and Rainbow Dash believes he created the Martingale persona to publish books that portray him as a hero. Rainbow confronts Caballeron about his new scheme to make Daring Do look bad, but Caballeron says he is just sharing his side of Daring Do's story with the public. Rainbow refuses to acknowledge Caballeron's claims, but Fluttershy offers to hear him out.
Caballeron explains that he and his henchponies unearthed ancient artifacts in order to preserve them in a museum, but Daring Do always intervened, refusing to team up with Caballeron and keeping the artifacts for herself. When Fluttershy mentions Caballeron's past attempt to sell an artifact to the highest bidder, Caballeron reveals he did so because Daring Do's actions caused his museum to go out of business. As Fluttershy starts to consider the true consequences of Daring Do's actions, Caballeron thanks her for listening to his side of the story and invites her to accompany him and his team on an expedition to the Tenochtitlan Basin. Fluttershy accepts Caballeron's invitation in order to find out which of the two Daring Do authors is telling the truth, much to Rainbow Dash's shock. Rainbow Dash hurries back to A.K. Yearling and brings her up to speed about what is going on. Yearling believes that Dr. Caballeron is going after the Truth Talisman of Tonatiuh, which cannot be reached without a Pegasus' flight, and that he tricked Fluttershy into joining him in order to obtain it. Discarding her A.K. Yearling disguise, Daring Do joins Rainbow Dash in her quest to stop Caballeron and save Fluttershy.
Deep in the Tenochtitlan jungle, Caballeron puts on a facade of wanting to preserve the local plant life and protect his henchponies from poisonous fruits for Fluttershy's sake. Fluttershy shares food with her new friends and pacifies the wild jungle cats before they can attack; Caballeron and his henchponies are impressed by Fluttershy's kindness and willingness to listen. Meanwhile, Rainbow Dash and Daring Do race to catch up with them before Caballeron can claim the Truth Talisman for monetary gain. Dr. Caballeron and his team reach the temple that houses the Truth Talisman of Tonatiuh. As they attempt to gain entry into the temple, Fluttershy gives Biff positive reenforcement and saves Withers from a swarm of fly-ders. Close behind them, Rainbow Dash and Daring Do run into Ahuizotl, who believes they are also trying to claim the Truth Talisman. Rainbow and Daring escape from Ahuizotl just as Caballeron and his team open the temple entrance, and Rainbow and Daring follow them inside. While Rainbow and Daring Do navigate the temple's labyrinth-like structure, Dr. Caballeron and his team quickly make their way to the chamber of the Truth Talisman of Tonatiuh. Caballeron, over-dramatically playing to Fluttershy's kindness, convinces her to retrieve the Talisman with her flight. When Fluttershy triggers a booby trap and nearly falls into a pit of lava, Caballeron and his henchponies save her.
Just as Caballeron claims the Truth Talisman for himself, Rainbow Dash and Daring Do appear and demand he relinquish it. Fluttershy tries to convince them that Caballeron and his henchponies simply want to put the Talisman in a museum, but Caballeron is compelled by the magical properties of the Talisman to tell the truth. He reveals that he did indeed trick Fluttershy into joining him at first, but during their time together, he and his henchponies came to value her kindness and friendship. Just then, Ahuizotl appears and commands a group of stone gargoyles to attack the temple intruders before trapping them inside the chamber. With Fluttershy's animal communication ineffective against creatures made of stone, Daring Do and Caballeron drive them off with bright light reflected off of a diamond artifact. The ponies all work together to escape the chamber and run into Ahuizotl again. They struggle to keep the Truth Talisman away from him, but he eventually traps them in a narrow dead end. As the ponies wonder how they will escape, Fluttershy decides to reach out to Ahuizotl the same way she reached out to Dr. Caballeron earlier, and she asks him why he is trying to destroy them. Ahuizotl takes the Truth Talisman and, influenced by its magic, explains that he is one of several guardian creatures of Equestria tasked with protecting the artifacts of Tenochtitlan, a task made difficult by Daring Do and Dr. Caballeron's repeated artifact thefts.
