Uma is at the playground, building a sand castle in the sandbox. Oobi and Grampu walk over to see her creation and compliment it. After putting some finishing touches on the sand castle and patting it down, Uma takes a plastic crown and gives it to Grampu. She names him the king of the castle.
Next, Uma takes a plastic ring, gives it to Oobi, and names him the prince of the castle. Oobi and Grampu wonder what Uma should pretend to be. She doesn't want to be a princess or a queen, so she takes a yellow construction hat and says that she will just be the castle builder. Oobi and Grampu laugh as she pats down her castle again.
A royal fanfare plays when Grampu and Oobi wear their crowns.
This is the only short with a character's name in the title.
While filming this short, the puppeteers had to wear goggles to keep sand from getting in their eyes. Tim Lagasse features a behind-the-scenes photo from this short on his website, showing him and Stephanie D'Abruzzo with goggles. (source)
According to Tim Lagasse, this episode was shot during the first week of filming for Oobi. (source)