Finding Dad is a Phineas and Ferb story that deals with Phineas' true dad, but with a lot more Phineas/Isabella romance. The fic is notable for being one of the few fics that has Phineas and Isabella get together during the summer vacation.
Seven years before the greatest summer ever, Campbell Flynn divorces Linda Flynn. Across the street, Manuel Garcia leaves Vivian and Isabella for a government job. Isabella runs over to Phineas' house and he promises never to hurt her.
Phineas wakes up from a dream, and overhears Linda and Lawrence talk about his true dad. Isabella wakes up, walks over to Phineas, and they decide to find their respective missing dads. Phineas and Isabella find out from Candace that Campbell is located in New Orleans. The young duo then tells Vivian about the trip. Phineas remembers that he has $500 earned from allowance and invention commissions, while Isabella has $300 from babysitting her cousins. Phineas and Isabella leave their families, but not before telling them. During the bus ride to Charlotte, Phineas begins thinking about how precious Isabella is to him.