With the kingdom in peril from the marauding Vikings, “Aguar” (Donald Crisp) sends his son “Valiant” (Robert Wagner) to safety in England where he is to attend the court of king “Arthur” (Brian Aherne). He is welcomed there, but quickly discovers that there is a duplicitous black knight who is consorting with the Norsemen to capture him. Who is this mysterious figure? Meantime, he is assigned to the staff of the gallant “Sir Gawain” (Sterling Hayden) in whom he confides his suspicions of “Sir Brack” (James Mason). Naturally, his mentor doesn’t believe him and in despair, the young Prince tries ...