Captain Uniqua and Lookout Austin are brave pirates, who seek a hidden treasure after finding half of a treasure map, without knowing that Pablo and Tyrone have the other half and are also looking for the same treasure.
Uniqua is first shown coming out of her house and into the backyard. She explains to the viewer how she is a scurvy pirate in search of treasure, with only half of a pirate treasure map. She sings the song "A Pirate Says "Arrr!". Uniqua draws a skull and crossbones flag in the sandbox as Austin comes out to greet her. Austin tells Uniqua that he will like to become a pirate as well, and Uniqua agrees to let him aboard her pirate ship. The two pirates run off.
The camera moves to Tyrone and Pablo, who are playing ball more on the left side of the backyard. When Pablo accidentally kicks the ball over near the sandbox, he runs over to it. He suddenly notices the skull and crossbones Uniqua had drawn earlier. Pablo exclaims that pirates have come to the backyard, and tells Tyrone that the two of them should become pirates and find treasure, just for all the money and gold they would then have. Tyrone likes the idea, and agrees. The backyard transforms into the ocean, in which Pablo and Tyrone are sailing across in a large pirate ship.
Pablo is a peg-legged pirate in charge of steering the ship. He is turning the boat's wooden wheel at every turn. Tyrone is the lookout. Tyrone asks Pablo what they would do if they ran into other pirates, and Pablo answers with "make them walk the plank!". They start to sing the song "A Scurvy Pirate". The camera turns to Uniqua and Austin, further into the ocean, on a pirate ship as well. Uniqua is the captain and Austin is the lookout. Uniqua repetitively asks Austin if he sees any islands or pirate ships. Austin answers "no" and "not yet" frequently. After a long while, they come to the area of the ocean that Tyrone and Pablo are sailing in. Austin spots them immediately, as Pablo spots him and Uniqua.
Uniqua and Austin are ordered to walk over to the other pirates' ship, and they do so. Austin, with his telescope, and Tyrone, with his, are told to fight with them. Tyrone knocks Austin's portable telescope out of his clutch, winning the match. Uniqua and Austin are sentenced to walk the plank, due to their losing. The both of them obey. As Uniqua jumps off the edge of the board, she falls on her bottom. She looks around, realizing that she is on a desert island. Austin jumps off shortly after. The two scurry off into the more forest-like center of the island.
Pablo and Tyrone have waited a matter of time since making the other pirate pair walk the plank. Their boat is still in front of the island, even though the two have no clue that they are. Pablo gets tired of waiting to here a pirate sink, so he looks at the island to check for the other pirates. He suddenly realizes the fact that they are floating right near the exact island shown on their treasure map. Pablo immediately tells Tyrone, his partner, to run after those other pirates and get that treasure before Uniqua and Austin do.
Pablo and Tyrone dash on to the island. They catch up with the other two. As Uniqua looks at her half of a treasure map, Pablo thinks about how the other map looks. He comes to think that it is the other half of theirs. Pablo tells Uniqua, and they both decide to team up and find the treasure together. The four pirates journey off into the island's center, following their full map. They sing the song "Treasure".
The team comes to a stop as the path they are following leads to a massive pit of gobbling mud. They look around for a way across. They spot a log. Pablo is pessimistic because he has a peg leg. But Tyrone tells him he can do it. Uniqua walks across it slowly, while starting the song "Falling Off A Log". She comes to the other side and tells the rest of the crew that it is safe to cross.
Tyrone crosses next. He sings the second part of the song. Austin crosses third. After three out of four pirates have crossed, Pablo works up the courage to go. He walks across slower than any other pirate, because of his peg leg. He sings the last part of the song. Pablo stops singing as he begins to lose his balance. "Whoa!" he yells. After the others give Pablo more confidence, he gets on track again, and crosses safely.
The pirates are now deep into the island's center. Austin thinks he's spotted an "X", but Tyrone points out that it's actually a "T". The team thinks about this, knowing that no one would bury treasure under a "T". They advance forward, and Austin excitedly spots out a "U". Pablo finds a "V", then Tyrone finds a "W". They all now realize that the sand trail consists of letters from the alphabet. Tyrone goes through the list "T, U, V, W.", then Uniqua then spots the "X". She starts to dig with a shovel. After a lot of digging, her shovel hits something hard. They uncover it, revealing the item as a treasure chest. The pirates open it and find a large diamond. They then bury the precious jewel.
But then, they realize that other pirates will just come and find the treasure. After a lot of thinking, Uniqua decides to mark it with a "Y". The other pirates agree and help her cover the chest up. Pablo's stomach growls, and Uniqua offers that the four present Backyardigans could come over to her house for a snack.
The island transforms into the backyard once again as the four friends sing the Backyardigans' end song. They then run into Uniqua's pink house for a snack. Uniqua opens the door and exclaims, "ARR!".