It's the summer solstice, so Phineas, Ferb, & 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've set out to do, leading them to get some encouraging words, in the form of a duet, from Clay Aiken and Chaka Khan. Meanwhile, Dr. Doofenshmirtz takes a father-daughter trip to Tokyo with Vanessa.