Thueringen, 804 A.D. An orphan boy named Bengel lives in an abbey and is teased by the nuns because of his ugliness. The boy nurtures the Black Knight back to health, though the Knight is thought to have the plague and is therefore shunned by everyone else. The Knight tells Bengel about the missing Bogumil, son of the Slav king, Slavomir, who, per order of Charlemagne, was to marry the Thueringian Margrave's daughter Reglindis. He also asks Bengel about his ancestry. Bengel now believes that he is Bogumil. He goes to the castle, where he meets a beautiful girl who thinks he's just as handsome. It is Reglindis, and she is blind. She finds his inner beauty and devotes herself to him. However, her father wants to get rid of him. Bengel barely avoids death twice, the Black Knight reveals his identity with a flourish to Bogumil, and everyone lives happily ever after.