Spurred by love for the beautiful Lady Linet (Patricia Medina), humble sword-maker John (Alan Ladd) begins training to become a knight. When a raid on the castle leads to the death of Linet's mother and the incapacitation of her father, the earl of Yeonil (Harry Andrews), John's chase after the evildoers is misunderstood as cowardly running away. Transforming himself into the mysterious Black Knight, John infiltrates the castle of King Arthur (Anthony Bushell) to unmask the ne'er-do-wells.