When Dr. Doofenshmirtz's newest inator blasts directly into the Flynn-fletcher's back yard life and love will change forever for Phineas, Ferb, and Isabella.

After a brief mention of their biological father, Phineas and Candace grow curious and decide to do some research, while Ferb wants nothing to do with it for unknown reasons. Little do the Flynn-Fletcher siblings know what they're getting themselves into. (Rated T for language and angst. TW later on)

The Avengers Endgame of Phineas and Ferb Fan Fic