When a thunderstorm causes a blackout at the Flynn-Flecther house Phineas, Ferb and friends fall into the basement where they discover an old book that tells the story of King Arthur. In the kingdom of Camelot Arthur (Phineas) was the lowly page of the arrogant Sir Lancelot (Buford). During a jousting tournament when Arthur went to get Lancelot's sword, he frees the magic sword, Excalibur, encounters the wizard Merlin (Ferb), and becomes the King of Camelot. Now Arthur is living the good life, including outshining Lancelot and engagemnet to the beautiful Princess Guinevere (Isabella). But will he be prepared for the scheming witch Morgan le Fay (Candace) and her mysterious enforcer the Black Knight (Perry).