The film begins in Mexico with an owl hovering, before transitioning into a tween age demigod called Punguari and her mother tells her to pretend to have fun, but the Punguari wants to become a full god, as she is now 12 years old, but her mother doesn't allow it. The Demigods father and mother ask her to forget about being a god and she apologizes and goes on an adventure through a magic door. The demigod puts on a mask and she turns into a full god, before unleashing magma on the village and exploding it. The demigod turns to stone.Meanwhile, in Great Lakes city, Ronnie Anne sneaks out with her skateboard and skates down the town on her 12th birthday. Ronnie Anne meets her best friend, Sid Chang and plans to skate at the super skate park, before her mother, Maria tells her to come home quickly for a birthday surprise, so she does.When Ronnie Anne gets back, she pops through all the balloons and into the apartment, where every member of the family celebrates her birthday in their own special way. Ronnie Anne then opens her presents and Frieda is about to tell her a surprise, which is ultimately spoiled by CJ that they are going to Mexico all summer, which Ronnie Anne doesn't want to do, but gets forced into it anyway. Whilst on the road, Ronnie Anne looks sadly out the window.Maria tells Ronnie Anne that she has made an entire itenaray of their whole vacation, before crashing into a cactus patch and get out the van in Mexico, during the festival of the new fire, where there is a big bonfire. Bobby goes and does all sorts of activities with a paper version of his dad and he begs Carlotta to teach him how to take a good selfie.Ronnie Anne goes to a stall and wants to buy a crystal, but Maria prevents her and when she is gone, Ronnie Anne gives the man a box full of money. Momma Lupes boat paddles the family across the pond to her house and Maria reminisces about the good old times. Carlos then tells the family about Mount Punguari and the story of Pungari and how she wanted to become a proper god and how she was turned into the mountain. If she is freed, the city would be cursed.Now inside the house, Momma Lupe tells CJ and Carl that she loves fireball, but quit due to her team breaking up, but decides to teach them how to play. Ronnie Anne facetimes Sid, who is skating at extreme A and Sid arranges a skate along together and Ronnie Anne plans to skate at Mount Pungari.The next morning, Maria wakes Ronnie Anne up and asks her to help make masks, but she sneaks off to skate instead. Frieda attempts to paint, but gets distracted by Carl and CJ training fireball. At Mount Punguari, Ronnie Anne calls Sid and the two skate down together, until Ronnie Anne trips and falls on a rock. Ronnie Anne notices her crystal has changed and an earthquake happens. A girl is trapped on a tree branch and Ronnie Anne frees her and it turns out she is Punguari. Ronnie Anne shows her family her new friend, pretending her name is Shara and about what happened, but Maria doesn't listen and believes Ronnie Anne isn't mature enough to do her own thing. Ronnie Anne tells Carlos what happened and he gets out another book, revealing that Punguari is after the mask of many places and the two girls rush off to grab it before she does.Maria gets mad at Ronnie Anne and teaches Maria to throw her chancla, but misses the target. It is revealed that both Maria and Rosa did their own things when they were Ronnie Anne's age and Maria finally hits the bottle.Ronnie Anne and go to the museum to join a tour, but go down to the basement and search for the mask and Maria asks to talk to Ronnie Anne and Shara the girls agree on them being old enough to do their own things and the duo start dancing to Twelve is midnight together, Ronnie Anne's crystal begins glowing and it leads her to a picture of the mask and she discovers that the gem is the same as the masks. A door opens up and the two of through and tells Ronnie Anne to put the crystal in and Shara reveals herself as Punguari as she connects her face to the mask and she goes to complete her ceremony.Back at Momma Lupes house, Maria looks for Ronnie Anne, while Ronnie Anne is still stuck in the secret room and Ronnie Anne begins to cry, before hearing humming and a window opens to her Abuelo and she tells the family that she is trapped and asks her family to come and save her. The family sneak out to the museum in the night, and they trap the security guard. The family arrive at the secret door and try freeing Ronnie Anne, but end up getting stuck in there themselves. Ronnie Anne smashes a vase, which reveals that Ucumu is the true bad guy and they go to stop him. Punguari uses the mask to create a thunderstorm and twisters, causing panic in the town.The temple begins to rise and Punguari prepares to release Ucumu. Ronnie Anne claims she can stop her and skateboards up to her, with the help from Sergio and the other birds and Maria chases after her in the van, which ultimately stops in the mud, but doesn't give up. Ronnie Anne asks Punguari to stop and Punguari turns on her, but Ronnie Anne says her mother turned her into a mountain to protect her from Ucumu. Punguaris parents tried to defeat him, but failed. Maria comes after Ronnie Anne, but holds on for dear life as she is about to fall into lava, but Maria uses her list to recover to safety and Punguari, who is a giant dog drops them off at the family.Ronnie Anne plans to stop Ucumu with a giant flaming Chancla, but Ucumu arrives too quick. Ronnie Anne and the family plot to stop Ucumu and they set out to get the things they need. Ronnie Anne rides Punguari while the others distract Ucumu with a plane and Lalique digs up a very big Chancla from a grave stone. The family go back to the house, only to fall down the floor and they all pile upon each other to reach the fire and Bobby uses his paper father to collect it.Ucumu and Punguari continue fighting and Punguari realizes that her parents are alive and she gets whacked by Ucumu, who then tries to attack the plane, but fails. Ucumu begins throwing giant balls of fire and summon other fire demons, which are soon defeated. The family begin fighting off the monsters and Ucumu crushes Punguari. Maria throws the Chancla, as CJ and Carl use their fireball training to connect the flame to the Chancla, which hits Ucumu, melting him to bones. Ucumu begins running towards Ronnie Anne who burns what is left of Ucumu and Punguari uses the staff to destroy her temple, ensuring Ucumu never comes back and freeing Punguaris parents and they tell her she did good.Maria runs to Ronnie Anne and they apologize to each other and Maria and Punguaris mother tells them they are ready to let them go and clean up the town.The festival of new fire is happening and Ronnie Anne calls Sid and Maria gets Ronnie Anne another, normal gem and the film ends with Punguari as an owl flying with her parents, during a fireworks display.