I was sorry to hear that Mary Stewart is dead, at the age of 97.
She was a writer of romantic and Arthurian novels who was never afraid of crossing the border into the fantastic. She had a wonderfully sure voice and a way of using tiny descriptive details to make even the most implausible things believable.
Some of her romantic novels also edged into fantasy, especially Touch Not the Cat (1976) which features hereditary telepathy. Many of her other romance novels used fantastic elements quietly and without any fuss, even though the books were set in the real world. Best of all these details were used as if she found the elements of the fantastic exactly as appropriate as any other elements to insert into the story she was telling. This isn't uncommon today, when the presence of paranormal romance has encouraged writers of romance to insert such things, but it was very unusual in her time and generation. Stewart is also to be commended for how well she dealt with the fantastic, and how seamlessly she integrated it with everything else. There's a lot to be learned from her technique there. Being aware that she would use the fantastic when appropriate made all of her novels more enjoyable for me—she was prepared to open up the space of possible answers to mysteries, even where the answers didn't go in that direction.
Her Arthurian novels put magic in a very interesting place in the worldbuilding—not at all where a fantasy writer would have put it, yet treated consistently and solidly as part of how the world works. Prediction is accurate, but being able to predict is not reliable. Other magics are also real but difficult. The books purport to be set in real history, but what is known about the real history of Dark Age Britain makes this in itself a speculative venture. Stewart has speculated, but based on historical and archaeological research. The Crystal Cave is told from the point of view of a young Merlin and as much as White or Malory shaped my perception of what Merlin can be. I grew up on these; they weren't my first Arthuriana, but they were close to it.
Both The Crystal Cave and The Hollow Hills won Mythopoeic Awards, and it's good to think that she had this recognition and welcome from within our genre. These books have been widely influential, and continue to be read and enjoyed, as are her more mainstream books like Nine Coaches Waiting and The Moon-Spinners.
Jo Walton is a science fiction and fantasy writer. She’s published a collection of Tor.com pieces, three poetry collections and nine novels, including the Hugo and Nebula winning Among Others. She has a new novel, My Real Children, out soon. She reads a lot, and blogs about it here irregularly. She comes from Wales but lives in Montreal where the food and books are more varied.