A modern prose adaptation by Douglas Hill.
Follows the adventures of twelve knights, each an example of a different virtue, as they undertake difficult quests for their queen.
Douglas Arthur Hill (1935–2007) was a Canadian science fiction author, editor and reviewer.
He is probably best known for his Galactic Warlord (The Last Legionary) quartet of novels, supposedly produced as the result of a challenge by a publisher to Hill's complaints about the lack of good science fiction for younger readers.
Douglas Hill. Wikipedia.