In 1983, Stewart published a fourth instalment in the series: The Wicked Day.

In The Hollow Hills (1973), Merlin recounts Arthur's birth and boyhood until he is made king.

In Stewart's obituary, Anita Gates of The New York Times described her as an "author of romantic thrillers who jumped genres in her 50s to create an internationally best-selling trilogy of Merlin books, reimagining the Arthurian legend from a sorcerer’s point of view.

The trilogy introduced her work to a new generation and, in many cases, to male readers for the first time.

… The books, set in the fifth century, were praised for their unusual blend of fantasy and historical detail.