Thuringia, 804 A.D. An orphan boy named Bengel grows in an abbey with no knowledge of his family or origins. Although everyone else shuns the mysterious Black Knight, who is thought to have the plague, Bengal nurses him back to health. The knight tells Bengel about the missing Bogumil, son of the Slav king, Slavomir, who, per order of Charlemagne, was to marry the Thuringian Margrave's daughter Reglindis. When the knight asks Bengel about his ancestry, Bengel comes to believe that he must be Bogumil.

When Bengel travels to the castle, he meets the lovely but blind Reglindis, who finds his inner beauty and devotes herself to him. Her father, however, wants to get rid of him. Bengel barely avoids death twice before he finally learns the identity of the Black Knight and the truth about his past.

This children's film is based on the lyrical drama King René's Daughter by Danish author Henrik Hertz.