The film opens at Burnish Industries in China. A yeti (voice of Joseph Izzo) escapes from his holding cell and proceeds to run from the building. Dr. Zara (voice of Sarah Paulson) and the mercenary captain (voice of Rich Dietl) chase after the yeti, but he manages to break out. Once outside, he hums, which triggers his powers that allow him to burst through the gate and run into the city. The yeti manages to find a place to hide, but he becomes sad when he sees a billboard for Mount Everest.
Teenager Yi (voice of Chloe Bennet) lives with her mother (voice of Michelle Wong) and her Nai Nai (voice of Tsai Chin). It has been a while since Yi’s father passed, and she hasn’t been as close to her mom or Nai Nai because of it. She takes on several odd jobs (dog-walking, babysitting, garbage removal, etc) to save up money to take a trip across China that she wanted to take with her dad. Her childhood friend Jin (voice of Tenzing Norgay Trainor) is more concerned with his social life, and Jin’s cousin Peng (voice of Albert Tsai) doesn’t have other friends to play with. Yi also keeps a violin that belonged to her father and still plays it every now and then. While on the roof, she starts to play as she looks over the city, but a helicopter searching for the yeti comes by and knocks Yi off her feet, causing the bow to slide to where the yeti is resting. Yi freaks out when she sees him, but when she sees that he is scared and injured, she realizes that he is not harmful.
Mr. Burnish (voice of Eddie Izzard) is angry that his yeti has gone missing, as he was hoping to unveil the creature before a special presentation. Zara promises to find the yeti and bring it back safely.
The next day, Yi gets some of Nai Nai’s pork buns and brings them to the yeti, who devours all of them in one gulp. Yi then runs to the pharmacy to get supplies to tend to the yeti’s wound. She spots Zara, the Captain, and the other mercenaries running around trying to look for the yeti, so she hides before going to help the yeti. Yi then notices that the yeti keeps looking at the Everest billboard. Realizing that he wants to go home to his mountain, Yi decides to name him Everest.
Later, Yi brings her violin out to play some music for Everest. He hums again, causing his magic to bring a wilted flower back to life. Jin and Peng go to the roof to look for Yi and find Everest playing with her, but from Jin’s perspective, it looks like Everest is eating her. He calls the cops, which Zara and the mercs overhear on the scanner. Soon, the mercs fly toward the roof and spot Everest. Yi helps him get away, with Jin and Peng following. Yi and Everest make it to the top of another building with the mercs cornering them, but they are saved by the building’s lights going off as they do every night. This gives Yi and Everest a chance to make it to the docks where Everest hops on a boat to go back home. Seeing how frightened he is, Yi hops on the boat to join him. Peng runs after them and is caught by Everest, while Jin reluctantly joins to protect Peng. He tells his mom he took Yi and Peng to Beijing for a college tour.
Everest and the kids end up in a crate of sodas as the boat stops at an island. Their crate gets on a truck, but they all fall off of it after Peng and Everest get too hopped up on soda. This leads to them having to walk to the mountain to get Everest home. Jin complains because he is hungry, and Everest hums again to cause some blueberries to grow. However, they start to grow to humongous sizes before they start flying and hitting the kids as they try to run away. They end up resting for the night, with Yi noticing that Peng and Everest get along so well because Everest is basically a child who misses his family. Jin makes an unintentionally insensitive comment about Yi becoming distant from her mom and Nai Nai after her father passed, which upsets her.
Burnish, Zara, the Captain, and the other mercs make it to the island, and they follow the trail of soda cans until they have a lead as to where they may find Everest. Burnish, not having stepped out of the comfort of his home and company for so long, begins to admire nature.
The gang starts making their way further, only for Burnish’s drones to spot them. Everest causes a dandelion to grow big enough to float them away, but Jin fails to jump after them and plans to meet the others in a village by the river. Jin is found by Burnish and his team, and they allow him to stay with them at their camp.
Yi, Everest, and Peng land their dandelion in the desert, leaving a family of turtles with plenty of food. They stop to rest again, but Yi feels that this whole mess is her fault. They then notice fish swimming upstream in the river, and Yi tells Peng that these fish don’t give up, and so they don’t have to give up either. They proceed to keep moving.
Jin can’t sleep and he begins to walk outside. He overhears Zara talking to the Captain. She drops her British accent and reveals that she never cared to bring Everest home safely, but rather to profit off of his existence, and she doesn’t care if she has to hurt the children to get him back. Jin tries to steal a motorcycle, but it rides off a cliff from under him. He ends up walking and going through treacherous terrain until he finally finds a vendor that gives him a boat in exchange for his phone.
The other three board a train that takes them to the village. Yi and Peng try to sneak Everest through the crowd with the other yaks, but Burnish and his team have spotted them. Jin arrives in time to get Yi on the boat, while Peng causes the yaks to stampede and create a diversion. He and Everest join Yi and Jin, but the Captain turns the van with him, Burnish, and Zara inside into a water vehicle. They chase after the heroes, so Everest removes the boat engine and hums to send the boat sailing further. They hit the land, but Everest’s magic causes the field of flowers to create a tidal wave that pushes them to safety. Even Burnish is amazed at this power.
The gang crashes their boat on another island. Yi’s violin is broken, and she runs into the forest. Jin follows her and asks if she is okay. She expresses her whole problem with her father’s passing, and her distance from her mom and Nai Nai. Yi even admits that she hasn’t cried over her dad’s death yet. When they get back to Peng and Everest, they find that the two helped fix Yi’s violin by using Everest’s hair as strings, giving the violin magic powers. Yi then looks at the pictures she had saved in her case of all the places she wanted to visit with her father. It turns out all the places they have just been to in their adventure WERE all those places, but there is one place that she hasn’t seen yet. The gang moves forward until they reach the Sichuan Buddha statue. Yi becomes emotional and starts to play “Fix You” (as her father did) on the violin. The magic from Everest’s hairs causes the statue to become covered in flowers.
As the heroes near the mountain, they are found by the mercenaries on a bridge. Everest runs to the top of the bridge and uses his magic to protect the kids. Burnish sees this and has a flashback to when he first saw yetis. He saw the mother yeti protecting her children, and he knew they were good creatures. He tells Zara that they have to bring Everest in safely. Instead, Zara tells the Captain to tranquilize Burnish. She then has the other mercs tranquilize Everest, causing him to fall to the bridge. Zara tries to use a cattle prod on him, but Yi attempts to fight her off. Zara ends up pushing Yi over the bridge, which Jin and Peng witness as Zara takes them as her prisoners. They board Everest in a cage and start to head out.
Yi holds onto a rope on the bridge. She pulls herself back up to the top and grabs her violin. She plays it to use the magic to revive Everest. He bursts out of the cage, stopping the mercs in their path. Yi runs over there as Everest frees Jin, Peng, and Burnish. He uses his powers to create large icicles that scare off the mercenaries. However, Zara and the Captain are now determined to take Everest in, dead. She rams the van into Everest, hitting the side of a mountain. This causes an avalanche that sends Zara and the Captain falling to their deaths. Everest is unharmed. Burnish tells Everest that he is an amazing creature, which is why the world must never know that he exists. He proposes to take the kids home, but Yi says she promised to bring Everest home first.
Everest uses his magic to create flying cloud creatures that guide everyone to the mountain. There, they find enormous yetis that are Everest’s family. He runs into their arms, and his parents respectfully nod to Yi in gratitude. The kids bid their friend farewell.
Burnish takes the kids home. Yi runs to hug her mom and Nai Nai. They later have dinner together, with Jin and Peng coming over. Peng brings in a box left to them from Burnish, with equipment for their next adventure. They then sit to have Nai Nai’s pork buns, which Peng claims to love more than anyone. Yi says she knows someone else who loved them just as much. As the family eats, the last thing we hear is Everest humming.