User blog comment:HyperHearts58/Any Ideas?/@comment-2053274-20101015171212

Phineas, Ferb and friends gets hit by one of Doofeshmirtz's rays and is transported to Earth in 100 million years(Which is ruined except for the technology centre). They have to travel across Earth to get to the technology centre but when they find out there is no way back from the future Phineas goes mad. I don't know how they get back but it probably involves Doofenshmirtz again.