These are not the nuclear exchanges Walton and I were arguing about a moment ago. Those ones might have occurred - in the end she managed to do without them - in Half A Crown, the final novel of her Small Change trilogy. All three of those books are about Britain's gradual, chillingly plausible slide towards facism in the wake of a brokered peace with Nazi Germany: a small change that changes everything.
So that's four novels about alternate versions of mid-20th century Britain. Why am I saying Walton is hard to pin down? Her books do tend to be set in Britain - she's Welsh, though she has lived in Montreal for the past 12 years - and they often play games with recent history.
"I love space opera. I love all that side of science fiction. But I have this great problem with it, which is that it's really difficult to research. If I have to stop and check everything it slows me down to the point where I grind to a halt. If I had a proper scientific background, I'd be able to work out these things myself, the way I can work out historical problems. I did my degree in classics and ancient history. You know - the useful stuff."
But as well as being a somewhat prolific writer - "I know some writers who like having written, they like being writers, but they don't actually enjoy the process, whereas I just love writing, I get a real kick out it" - Walton is a passionate and voracious reader. She won the Hugo and Nebula awards two years ago for Among Others, a heart-piercingly moving fantasy novel about the pleasures of reading. Its heroine, a bereft and crippled teenage girl called Mori, has a relationship with the books in her life that readers all over the world have recognised.
"To a certain extent Mori is me when I was 15. I used a lot of autobiographical stuff in that book, and yeah, the way she reads is the way I used to read. I don't have time to read as much as she does any more."
The thing about having been this sort of reader her whole life - and in particular, this sort of reader of science fiction and fantasy - is that Walton is deeply versed in how genre fiction tends to work. Her most recent book before My Real Children was a collection of short essays, What Makes This Book So Great: Re-reading the Classics of Science Fiction & Fantasy. Part of what drives her writing is the pleasure she takes in playing games with reader expectation, and one consequence is that even
her Small Change books, which form a single continuous story, do not feel like they belong to a single genre.
"Most of my books are playing with genre in some way. So for the Small Change series, Farthing is trying to use both country-house mystery and science fiction conventions. In Ha'penny it's thriller pacing, and Half a Crown is doing a dystopic thing. It's interesting to play with that. I can keep the story in tension with genre expectations and so I don't get bored."
It was her teen reading that initially fed Walton's desire to write. "I think like a lot of people I felt intimidated by the best things I read, and then read things that are less good, and thought, well, that's possible. I might not be able to write as well as Tolkien, but I could write as well as Anne McCaffrey!"
She wrote all through her teens, before giving up in her 20s. "I showed the thing I was working on at the time to my first husband, and he said it was awful, which it probably was. And I believed him, and stopped trying to write, and I didn't write again for eight or nine years. I always tell people this, because there is this piece of wisdom out there that if you're a real writer you'll keep writing no matter what, and it's just not true. You can stop and then start again. I think it's useful for people to know that. You actually can start again."
My Real Children (Constable & Robinson $36.99) is out now.