As city girl Ronnie Anne Santiago (Izabella Alvarez) gears up for her anticipated "Summer of 12" at Xtreme Eddie's alongside her best friend Sid Chang (Leah Mei Gold), she is taken aback by her family's sudden announcement of a trip to Japunda, Mexico. Despite her initial disappointment, this unexpected adventure leads her to the intriguing abode of Mama Lupe (Angélica Aragón), where a captivating shopkeeper introduces her to a mystical necklace that supposedly holds the last connection between humans and gods. Though her mother Maria (Sumalee Montano) dismisses the necklace's validity, Ronnie Anne, caught up in the allure, discreetly purchases this cherished trinket.
Upon arriving in Mexico, Ronnie Anne is awe-struck by the magnificent mountain known as Punguari. According to Bobby Santiago (Carlos PenaVega), this mountain embodies the spirit of a rebellious demigoddess who was deprived of her divine legacy. Renowned for her mischief, Punguari once absconded with a magically charged mask, only to be petrified by her mother Sisiki when calamities began to ensue. The tale warns that if Punguari is freed from her stony prison, dire consequences would befall the land.
The following day, Ronnie Anne expresses her respect for Mount Punguari as she synchronizes her skateboarding skills with Sid over a video call. However, a sudden misstep causes the necklace to shatter, unintentionally unleashing Punguari from her ageless slumber. As Ronnie Anne grapples with the ramifications of her actions, she encounters Shara (Paulina Chávez), a girl whose leg has been pinned under a fallen branch due to an earthquake. Together, they face the ire of Ronnie Anne’s mother, who admonishes her for her reckless behavior.
Later that night, Maria expresses her frustrations to Mama Lupe, who then decides to impart a lesson to Ronnie Anne on the art of chancla throwing. In the meantime, Ronnie Anne and Shara embark on a secret expedition to a local museum, where they stumble upon an entrance to the realm of the mask. Unbeknownst to Ronnie Anne, Shara is actually Punguari in disguise, and she seizes this opportunity to reclaim the mask, ultimately trapping Ronnie Anne within the mystical realm.
Desperate to find his granddaughter, Hector (Fabio Tassone) resorts to using a magical mirror to locate her while she narrates her plight to her worried family. They devise a stealthy plan to infiltrate the museum under the veil of night, with hopes of rescuing her from the grasp of both Punguari and Ucumu, the formidable God of the Underworld, whose ascent to power is secured by Punguari’s reckless wielding of the mask.
Soon, Punguari, empowered by the mask, metamorphoses into a goddess and commands a temple to rise from the depths of the ocean, like a leviathan emerging from the depths. But this newfound might comes at a cost, as the earth begins to tremble once more, releasing a wave of chaotic energy. Unwilling to stand by, Ronnie Anne bravely confronts Punguari in her splendid new temple, sharing the emotional truth that her parents had petrified her out of love and desperation to protect her from Ucumu’s wicked influence.
Amidst this turmoil, Maria narrowly avoids a treacherous fall and harnesses her quick wit, employing her itinerary as a makeshift trapeze to save herself just in time. Reunited with her family, they face the awakening Ucumu, who rises like an ancient giant. Joined by the Casagrande clan, each member contributes their unique abilities to fend off the impending threat, with Bobby’s group providing crucial reinforcements.
Amid Ucumu’s rally for dominance, Don Tacho, Mama Lupe’s unwavering caretaker, makes a heroic entrance, crashing his plane into the battle and clearing a path for the Casagrandes. Yet, just as Punguari is incapacitated by Ucumu’s sheer force, he attempts to drag her towards a dreadful portal on his mask, threatening to devour her very essence.
Determined to turn the tide, Maria leads a band of Chancla Warriors in raising a colossal chancla, while Frida (Roxana Ortega) unleashes her martial arts prowess upon Arturo (Carlos PenaVega)’s flame-imbued paper cutout. With immense force, the chancla strikes Ucumu, dismantling him into a mere skeleton, while Ronnie Anne seizes the moment to petrify Ucumu's minions, restoring order.
As Punguari regains her strength, she champions the sealing of the chasms with her temple, ensuring that Ucumu's dark powers remain buried under the earth. In the aftermath, Sisiki and Chipiri, once mere gemstones, are revived, reunited with their daughters while Maria and Punguari cherish the lessons learned and friendships forged.
Chipiri then employs his ancient magic to rejuvenate the land, bringing it back to its former splendor. To celebrate newfound harmony, the Festival of the New Fire marks its triumphant return to Mama Lupe's island, where Maria gifts Ronnie Anne yet another precious gemstone. Punguari, Sisiki, and Chipiri watch over the festivities from a distance, their hearts swelling with pride, knowing that their familial bonds have been irrevocably enriched through this unforgettable journey.
