Oobi is excited to show everyone a storybook he just made called "The Lost Umasaurus." As he reads the story, we see the story played out in an Oobi-style dinosaur world. Together, the dinosaurs help the Umasaurus find her way home to Grampusaurus. — NickJr.com (source)
Oobi is outside, drawing on a sheet of paper. He says hi to the viewers and explains that he's just finished writing a storybook. He calls for Uma, Kako, and Grampu, who come to see his book. Kako asks Oobi what the story is about, and Oobi offers to read it out loud. He calls the book "The Lost Umasaurus", and the main character is a dinosaur version of Uma. Uma gets really excited and asks him to start reading.
The next scene is set in the world of Oobi's book. It shows Umasaurus, who is stuck in some vines in a prehistoric forest. Oobi narrates as Umasaurus meets another dinosaur named Oobi-Rex, who helps her move through the vines by eating them. Umasaurus tells Oobi-Rex that she lives in a red house with her grandpa, Grampusaurus. She's lost and can't find her house.
Oobi-Rex offers to help bring her home. As they walk, Umasaurus spots a white fence that she recognizes. She tells Oobi-Rex that it's the same fence that leads to her house. The two friends sing as they follow the fence. The scene cuts back to Oobi, his family, and Kako reading the book. Uma has a lot of questions for Oobi about how Umasaurus will get home, but they'll spoil the ending. Grampu asks Oobi to keep reading.
The next scene shows the dinosaurs again. They come across a big boulder that stands between them and Umasaurus's house. They each try to push it out of the way by themselves, but it doesn't budge. Umasaurus gets desperate and starts to worry. She thinks that she'll never get home and will have to live with the rock forever.
Luckily, a third dinosaur named Dino-Kako comes by and offers to help. He says he's super strong and tries to push the rock by himself. When this doesn't work, he picks several leaves off the ground and eats them. Oobi-Rex questions him, and he explains that he needs "more protein". He tries pushing the rock again, but it still does nothing. Umasaurus asks the other dinosaurs to push the boulder at the same time.
The idea works, and Umasaurus soon finds her house. Her grandpa, Grampusaurus, is waiting for her there. He greets her and her new friends. They tell Grampusaurus what happened, and he figures that they all must be hungry. He gives them a bowl of brownies, which he calls "dino-snacks". Oobi finishes narrating the story and his family cheers. Oobi decides to give his book to Uma as a present. She thanks him and hugs him as the episode ends.