Phineas and Ferb Special Episode
The Phineas and Ferb Special Episode is, hence the title, a special episode of Phineas and Ferb. It has not yet been given a name, but it's the first crossover episode.
Candace spots Phineas and Ferb building a giant popcorn machine, and she finally gets them busted (for real this time!) and they are grounded for life and sent to their rooms. Candace decides to throw a party to celebrate, and invites all of her friends, including Jeremy and Stacey.
Phineas and Ferb are locked inside by Mom and Dad who build some anti-escape devices which prevents them from trying to leave the house. Candace is about to throw her party when Mom and Dad catch her, send her to her room and tell the party guests to go home. Candace has also been grounded.
The stepbrothers are building a robot called Butler-Matic 5000 which obeys their every commands. Candace catches them in the act, but the robot proceeds to paint her face red.