A fictional narrative is either a newly created story or a retelling:
Homer and the Greek dramatists retold myths;
Virgil retold the prehistory of Rome;
William Shakespeare retold already existing stories;
John Milton retold the Biblical narrative;
pantomimes retell familiar fairy stories;
new films or TV series retell the stories of superheroes;
Isabel Allende retold the story of Zorro;
several of Poul Anderson's works, e.g., The King Of Ys (with Karen Anderson) or Hrolf Kraki's Saga, are retellings.
However, the details of a retelling can at the same time constitute a newly created story, e.g., Poul and Karen Anderson's character of Gratillonius and his struggle to preserve civilization as the Roman Empire retreats. Although the Smallville TV series retells a modern American myth, it simultaneously presents a never before told story of complicated interactions between the Kents and the Luthors. Certain highly dramatic episodes of Smallville reinforce my impression that Poul Anderson would have been an ideal choice as a writer able retell this heroic myth. Anderson would have not only rationalized the story's inherent absurdities, without adding any more, but also realized its characters and their period.