Diluge country was in danger of being invaded by monsters. Princess Lina asked for a holy swordsman to save the country. Swordsman Night Earth, who rushed there, joins Ranger (Hunter) Luna, Magician Jupiter, and his grandson, Witch Milly, and heads for the Magic Cave Dungeon. While many monsters attack, the party meets the merchant Shelterkun, Knight gets the sword of light darkness and the shield of God and Demon, and Luna gets the bow of fire. The Lizard Mage, who controls it, manufactures a murder machine called Deathlord and names it "Iron Knight". Knight was overwhelmed by the power of the "Iron Knight", but in the battle he learned the true use of the sword of light and darkness. And when the final battle finally arrives, the mage lizard reveals his true form as a dark dragon, and the knight sacrifices his own life to face it.