"Uniqua, Pablo, and Tyrone are practicing their new dive at the Splashini Water Park. But will a Sea Monster in the dive pool prevent them from making their big splash?"
Uniqua, Pablo, and Tyrone are in the backyard wearing orange floaties around their arms. They introduce themselves as the "Amazing Splashinis", a group of synchronized swimmers hoping to successfully perform the Sextuple Somersault Splash (a move in which the divers jump from the diving board and do 6 somersaults while still in the air). The three sing "The High Dive". The backyard transforms into a large water park.
The Splashinis, now in complete diving uniforms, dash towards a large pool near a very tall diving board. The camera moves away from them and to a green sea monster swimming to the right side of the water, in the area leading to the ocean. The camera moves back to the Backyardigans. They all talk about the dive they will soon perform. The trio attempts to perform the dive from the lowest of the three platforms on the diving board, but do not succeed, only finishing three somersaults. They are disappointed at their failure, but try again on the second platform. They only finish four somersaults. The three get out of the water and sing "The Sextuple Somersault Splash" after discussing what they will do next: jump from the highest board.
The friends do so, but don't complete any somersaults because of the sea monster, who jumps out of the water and scares the swimmers. Pablo, Uniqua, and Tyrone splash down into the water and get out. Each one of the group are questioned. They start a long discussion about what the monster was, not aware of its real species. They suggest trying to lure it out by swimming in the pool as well.
Uniqua tries first. She jumps into the water. The sea monster jumps out of the water, and falls back in again. The characters know that it is green. Pablo then attempts. The sea monster jumps out of the water again. Pablo thinks he saw "wings", the monster's flippers. Tyrone pushes Pablo out of the water and tries again. The Splashinis now see polka-dots on the monster's back. They have an argument about what it is, and Uniqua ends it by telling the boys the only thing it could be is a sea monster.
Now, the Splashinis' problem is to figure out how to get the sea monster out of their pool. First, they try running around yelling "shoo!". The sea monster does not swim out of the pool. After their failure, Pablo decides to drive a water-boat while Uniqua and Tyrone water-ski to the ocean, as a plan to lure the sea monster out of the pool. The sea monster follows the three out to sea as they sing the song "Let's Go". Uniqua tells Tyrone and Pablo to ditch the innocent creature while he is not looking.
The Splashinis leave the sea monster jumping in and out of the water frantically in the wide open ocean. They drive their boat back to the water park and climb up the diving board. They fail to complete the sextuple somersault splash and find the sea monster again. Determined to get rid of the sea monster, Uniqua declares that they will have to scare him away. This time, the Splashinis wait by the stadium seating surrounding the pool. Uniqua places her finger in the water, and the sea monster comes out. Together, they pull out bullhorns and say "Boo!". Startled by their amplified voices, the sea monster jumps out of the pool, and starts hopping frantically around the park.
Realizing how much they scared the monster, the Splashinis start to look for him. Their search takes them from the pool area to a platform at the top of a slide by the edge of a waterfall. The Splashinis stop and try to find the sea monster. Uniqua spots him through the mist of the water, but the sea monster get startled again. He slides down the slide and the Splashinis follow him. A chase around the water park ensues, taking them under a tunnel, and through a large water jet system, where Uniqua, Tyrone, Pablo, and the sea monster are thrust high into the air by the shoots underneath them. They land at the top of a blue waterslide, where the monster and the Splashinis slide all the way back to the pool once more, splashing into the water.
The three friends come up to the surface. They start to look around to see where the sea monster went, but suddenly they find themselves on top of the monster's head as he emerges from the water, and keeps rising higher above the pool. The elevation gets high enough that Uniqua suddenly realizes that they can do the sextuple somersault splash. Uniqua tells Tyrone and Pablo to jump when she says 'go'. The Splashinis leap from the sea monster's head and plunge into the water.
Uniqua, Tyrone, and Pablo all realize now that they need the sea monster's help to perform their dive. Uniqua declares that there's only one thing to do: Ask the sea monster to be a Splashini. The three friends start to dance and sing "You'd Make a Great Splashini" to the monster. By the end of the song, they get the sea monster raise them them high above the water again. Together, the Splashinis successfully perform the sextuple somersault splash. Happy that they were finally able to do the move, the friends thank the sea monster for helping them, and say goodbye.
Pablo's stomach growled so Uniqua invites him and Tyrone over to her house for tuna fish sandwiches. The boys accept as the water park transforms back into the backyard. They all sing the end song and enter Uniqua's pink house. They all open the previously closed door and shout "The sextuple somersault splash!"