When they can't agree on details, Oobi and Kako decide to build separate forts. In the end, they realize it's much more fun to play together and they decide to connect the forts. — ABC Television (source)
Oobi and Kako are outside, marching to the beat of a snare drum. They decide to build a fort out of blocks. Kako wants to use yellow circles, but Oobi wants to use blue squares. Kako wants to place the fort on the left side of a table, while Oobi wants it on the right. This causes a big disagreement between them, and they each build their own separate forts instead. After finishing them, the boys brag about their forts. Oobi says his fort is stronger and better than Kako's, which makes Kako mad. Oobi tries to keep bragging, but Kako interrupts and says he's too busy to listen.
Later, Oobi's fort is shown with an emblem of a green handprint on it. Kako also has an emblem on his. Oobi says his fort is perfect and Kako says that his fort is "perfecto." Both boys sigh. Oobi sighs again, but in a louder tone, to prove how much "better" he is. Kako does the same. Uma walks in, wanting to play with them. The boys each want her on their side. Uma gets overwhelmed and leaves.
The boys get bored, and Kako decides to invite the viewers to his fort. Oobi invites the viewers to his fort and teaches them his secret knock: the second bar of "Shave and a Haircut". The viewers are brought back to Kako's fort, where he teaches them his own secret knock.
The boys continue to fight as Grampu walks by, wondering why there are two forts. He tells Oobi and Kako that fighting ruins the fun. Oobi invites Kako over to his fort. He compliments his fort, and Oobi gives him a square-shaped cracker. Oobi walks over to Kako's fort and gets a circle-shaped cookie. The boys decide to call a truce and combine their forts into a bigger one. They teach Uma and Grampu their secret knock, the whole of "Shave and a Haircut". Oobi and Kako announce that they're friends again.
In an interview segment, Uma asks the viewers if they like building blocks. Later, Oobi and Kako are in the backyard. They play a memory game with blocks in the shape of a circle, a square, and a triangle, which Oobi hides with a flowerpot. After the game, Kako disappears and is revealed to be hiding under the pot. Oobi laughs as the episode ends.