Phineas and Ferb want to do something today and they don't want to build anything. Isabella comes over and talks to the brothers about a new place called WaterWorld of Fun and Phineas decides to go there with Isabella. Candace has a sick day with the flu and is stuck in bed while Stacy takes care of her. Perry recieves a mission and as the same, it's Doofenshmirtz. Phineas and Isabella have found WaterWorld and decided to go swim in one of the large pools there and then Phineas says, "Hey! Where's Perry?" Perry the Platypus was trapped by Doofenshmirtz in the return of his suburban house. Doofenshmirtz wants to destroy the Earth so he put a time bomb into the center but it will not destroy the Earth. IT WILL DESTROY THE TRI-STATE AREA! Phineas and Isabella had loads of fun and were heading back home and they admitted their feelings for each other along the way. Phineas goes home and says, "This has been the best day ever." Perry is out of the trap and he destroyed the bomb in the center of the Earth and blew up Doofenshmirtz. The final word of Doofenshmirtz was, "Curse you, Perry the Platypus!" That concluded the fun and exciting final day of summer for Phineas and Ferb and Perry and Candace didn't even try to bust the boys this time.