Phineas, Ferb and the gang are all sick with a cold, so they decide to make it the best "sick day" ever by creating a live television feed to their friends' homes so that they can all enjoy a day of fun together. Meanwhile, Vanessa learns from her mom, Charlene, that her dad is picking her up from a party she is going to with her punk rock boyfriend Johnny and is worried that he will embarrass her yet again. However, Dr. Doofenshmirtz is busy trying to use his "Deevolution-ator" to drain Agent P's will power so that he can control him, and things get out of hand when Dr. Doofenshmirtz picks up Vanessa at the party, and it's up to Agent P to save the day.

Candace switches places with a princess who looks exactly like her, while the real princess helps the boys build a giant jukebox filled with live bands.