It's the summer solstice, so Phineas, Ferb, and their friends decide to travel around the world in one day in an effort to create the "biggest, longest, funnest summer day of all time". But not everyone believes they can actually achieve what they have set out to do, especially Buford. Candace tags along because Jeremy is on a trip to Paris, and she fears that there he may meet other girls. Also, Isabella finds her affections for Phineas sorely tested when his steadfast focus on achieving his goal puts pressure on her. Meanwhile, Dr. Doofenshmirtz takes a father trip to Tokyo, Japan with Vanessa, but sets out with Perry and Major Monogram to find her when she joins Phineas, Ferb and the others.

A musical in which Phineas and Ferb revisit the day they built a gigantic roller coaster in their backyard. Doofenshmirtz tries to pull the East Coast to the west using tinfoil and a huge magnet.

Agent P travels to the glamorous city of Montevillebad to stop Doof from winning the Grand Prix and collecting the prize money. When Doof uses his "I-don't-care-Inator" to sabotage the race and eliminate the competition, including international racing legend of Italian-Scottish-Swiss-Dutch descent Paolo Vanderbeek (Patrick Dempsey), Agent P must take the wheel and go head-to-head with Doof on the racetrack.

After facing the choice of imprisonment or community service, Doof becomes a teacher at Vanessa's school. Meanwhile, a trio of bugs embark on a journey to become the first insects to communicate with humans.