British-born author Susan Cooper, who won a 1974 Newbery Honor and the 1976 Newbery Medal for two novels (The Dark Is Rising and The Grey King, respectively) in her five-book contemporary fantasy series, The Dark Is Rising, is expanding another of her popular series. A quarter-century after publishing The Boggart, which was followed in 1997 by The Boggart and the Monster, Cooper reawakens this mischievous, ancient Celtic spirit in The Boggart Fights Back (McElderry, Feb. 27). In her novel, the alien sound of a motorboat jostles the Boggart from a deep sleep at the bottom of his Scottish loch—and just in time. The boat belongs to William Trout, an egotistical and greedy American entrepreneur, who plans to build a sprawling resort and golf course surrounding the pristine loch. Summoning magic, the Boggart and his cousin Nessie (of Loch Ness fame) join forces with Canadian siblings Allie and Jay, who are again visiting their grandparents in Scotland, to send Trout packing. From her home in Massachusetts, Cooper spoke with PW about resurrecting the Boggart, her creative process, and her close relationship with her longtime American editor, the late Margaret McElderry.

The Boggart and the Monster was published just four years after The Boggart. What inspired you to resurrect the Boggart after so many years?

I had fun writing the first book, and then had an idea for the second story—the Boggart discovers that his cousin had changed into the Loch Ness monster, and has been stuck in that shape for many years. After that, part of me wanted to go back to the Boggart, but I didn’t really have the right idea for a new story. The thought of doing a third book lingered in my mind, but sat in the back of my head for a long time.

What was the spark that finally ignited the plot of The Boggart Fights Back?

Long before Donald Trump ran for office, he of course developed many properties, and one day I came across an article about the kerfuffle surrounding a development he was pursuing in Scotland. He and his people had apparently treated the residents of the area poorly—and they did not want him there. And I began thinking about how this could be the focus of a third Boggart novel: what if someone like Trump came along and tried to build a development around the beloved loch and the castle that were the setting for the first two books? And what if the Boggart and the kids found a way to get rid of him?

With its environmental message, The Boggart Fights Back exemplifies your skill at meshing fantasy and real-world issues. Do you find that thematic balance satisfying as a writer?

I think that fantasy is always rooted in the real world—and then it takes off from there—and I suppose that is what I’m always subconsciously trying to do. I tend to deal with issues that kids will recognize from their own lives. This is something that Ursula Le Guin, who will be missed by so many of us, did so well. She was able to create a completely fantastic world and use that to express truths about the real world. Ursula was an amazing writer and an amazing person.

I’d say that she and Alan Garner, whose books are rooted in England, are two novelists I’ve always felt close to. I think instinctively the three of us tried to do the same thing—our writing is very much rooted in place. I remember meeting both of them in the 1970s—it was like meeting a sister and a brother. We tended to think in the same way, though we came at it from completely different places.

You developed a deep friendship with your late editor, Margaret McElderry. How would you describe her influence on your life as a writer?

Margaret was an extraordinary editor and my best American friend, and I miss her very much. I came to live in America in 1963 and she bought rights to my first children’s book, Over Sea, Under Stone, in 1964. I had written an autobiographical novel for adult readers, which my agent in those days couldn’t sell to any publisher. So I asked Margaret to read it and tell me what was wrong with it. And she said, “There is nothing wrong with it—it’s just that it is a children’s book, and I’m going to publish it!” And she did, under the title of Dawn of Fear, which is a story about growing up in wartime England in the 1930s.

And Margaret then published each of the Dark Is Rising novels?

Yes—and that sequence came about in an unusual way. About 10 years after I moved to this country, I decided that I wanted to write a novel about a boy who wakes up on his 11th birthday and discovers he can work magic. [The book would become The Dark Is Rising.] But I couldn’t make the story work, so it just sat there. And then one day I picked up Over Sea, Under Stone and re-read it, and it occurred to me that there was a link between that and the book I’d been trying to write, and that there should be other books as well. It was the most peculiar day of my life—it was as though I conflated several days into one! I sat down with a piece of paper and wrote down the titles of all five books in the sequence—as well as where they would be set and who would be in them. And then I wrote the last half page of the final book. I still have that piece of paper.

When you showed it to Margaret, was she on board with your mapped-out sequence?

She was. I was so fortunate that she was so supportive, and so very patient. She always said, “Take your time, and don’t worry about writing the ‘right’ book—just write!” And she also put up with my insistence about punctuation. I tend to punctuate by ear, and not according to the Chicago Manual of Style, which is the bible for copyediting in this country. Margaret let me do it my way.

On the final page of The Boggart Fights Back, as Jay and Allie head home to Canada, the boy tells the Boggart that they’re “coming back next year.” Might this mayhem-making cast make a fourth appearance?

It’s funny—when I wrote that line I thought, “Do you mean this?” I don’t think there will be another Boggart book. But I’m not sure. I suppose one can’t ever say never. For now, I’m hoping that this third book gives readers enjoyment, but also stirs people’s consciousness about the environment. I won’t get political—but one can only hope.

The Boggart Fights Back by Susan Cooper. SS/McElderry, $16.99 Feb. ISBN 978-1-5344-0629-2