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 shown drawing on a sheet of paper. He greets the viewers and explains that he has 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. He titles the book "The Lost Umasaurus", basing the titular character on Uma. Uma is flattered to hear this and asks him to begin reading.
The next scene shows the fictional Umasaurus, who is lost in a prehistoric forest. Oobi narrates as Umasaurus meets another dinosaur named Oobi-Rex, who helps her navigate through a group of vines by eating them. Umasaurus tells Oobi-Rex that she lives in a red house and cannot seem to find it.
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 is the same fence that leads to her house. The two friends sing as they follow the fence. The scene cuts to Oobi, his family, and Kako reading the book. Uma has many questions for Oobi about how Umasaurus will get home. Grampu asks him to keep reading.
The next scene shows the fictional dinosaurs again. They come across a boulder that stands between them and Umasaurus's house. They try to push it out of the way individually, but it does not move. Umasaurus becomes desperate at this point; she fears that she will live with the rock forever and never get back home.
Luckily, a third dinosaur named Dino-Kako offers to help. He claims to be extremely strong and tries to push the rock by himself. When this does not work, he picks several leaves off of the ground and eats them as Oobi-Rex questions him. He explains that he needs "more protein" and tries pushing the rock again. When it 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 grandfather, Grampusaurus, is waiting for her there. He greets her and her new friends. They tell Grampusaurus what happens and are given a bowl of brownies as a celebratory snack. Oobi finishes narrating the story and his family cheers. Oobi decides to give his book to Uma as a present. She thanks him as the episode ends.