During medieval times, Phineas and Ferb (or, Ferb-a-lot) set off on an epic quest to find the legendary sword, Excaliferb, so they can defeat the evil sorcerer, Millifishmirtz.

After losing a gift that Jeremy made for her, Candace is determined to recreate it before Jeremy realizes it's missing. Unfortunately, Candace can't remember what it looks like, so she enlists Phineas and Ferb to use their mind machine to enter into her subconscious and recapture the memory. Meanwhile, Doofenshmirtz's evil plan is to use his Underwear-Inator to take over the Tri-State Area, since everyone's greatest fear is being caught in public in their underwear.