King Roderick the Tyrant, having sent Lord Ravenhurst to slaughter the Royal Family of England, usurps the throne. The Black Fox and his band of rebels rescue the true king, an infant with the royal "purple pimpernel" birthmark on his backside. They harass Roderick and his men while guarding the baby. Lords Brockhurst, Finsdale, and Pertwee convince the king to seek alliance with Sir Griswold of MacElwain, by offering him Roderick's daughter Gwendolyn in marriage. Gwendolyn objects, for the castle witch Griselda fortold a more gallant lover.