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.