S03E46: Agent Doof

Candace's plans to watch over Phineas and Ferb backfire when Dr. Doofenshmirtz's "Babe-inator" turns her brothers into babies. After having an epiphany, Dr. Doofenshmirtz shows up at the OWCA to give up his evil ways. Agent P has no choice but to show Dr. Doofenshmirtz the ropes of the trade, but things quickly sour between the two after Dr. Doofenshmirtz accidentally exposes the identity of a fellow animal agent.