NG: There are things I can point at that probably set me off, the first of which was probably watching Doctor Who as a very small boy, and starting to realise that this man in this blue box was going to be functionally immortal, but his friends were going to be left behind in time. And also pets. You get pets and your lifespans do not match. I remember realising that as a very small boy, and thinking it was absolutely tragic. You know, my mouse has just died of old age and he’s three. The human lifespan seems incredibly short and frustrating, and for me, one of the best things about being a reader, let alone a writer, is being able to read ancient Greek stories, ancient Egyptian stories, Norse stories—to be able to feel like one is getting the long view. Stories are long-lived organisms. They’re bigger and older than we are. And the frustrating thing about having 60 years or 80 years or, if medical science gets fancy, 120 years, is that actually 1,000 years would be really interesting. You want to step back and go, “Where do you get this view?” and where we get it from is passing on stories, and handing down knowledge and experience. You sit there reading Pepys, and just for a minute, you kind of get to be 350, 400 years older than you are. I’ve always loved the idea of making things longer, changing perspective. And part of looking at things in the long term is also, I think, in a weird way, worry about the future.

KI: There’s an interesting emotional tension that comes because of the mismatch of lifespans in your work, because an event that might be tragic for one of us may not be so for the long-lived being. There’s an episode of Doctor Who that you wrote, called Doctor’s Wife, and one of the most haunting things about that was a passage where Rory and Amy are lost in some kind of weird time vortex thing. Rory ages enormously, he’s waiting like 70 years, while Amy is running around on the other side of the door . . . And she keeps getting visions of him grown really, really old and he’s been waiting for her, whereas for her, it’s just been like 20 seconds, and he’s saying, “Where were you, where were you?” Eventually he turns into just a pile of remains, human remains, and all you see is an angry, bitter piece of graffiti scrawled up on the wall, maybe in blood, for all we know. His love has turned to hate, because he just waited and waited for her.

Recently I’ve been interested in the difference between personal memory and societal memory, and I’m tempted almost to personify these two things. A society, a nation, goes on and on, for centuries: it can turn Nazi for a while and cause mayhem. But then the next generation comes along and says, you know, “We’re not going to make that mistake again.” Whereas an individual who happens to live through the Nazi era in Germany, that’s his whole life.

NG: If you’re going to try and tell one of those stories, then the urge comes to start figuring out a way that you can have a conversation between somebody who can see the big picture, or is the big picture, and somebody who is in some way a brick in the wall. One of the most beautiful things about fiction is that you can have those conversations if you need them.

KI: In those cases being able to resort to fantasy opens things up enormously. I’ve often done this, even if it doesn’t look so obvious, even if there aren’t things that look like mythical creatures. Creating an incredibly stuffy English butler in The Remains of the Day, I was very aware that I was taking something that I recognised to be a very small, negative set of impulses in myself—the fear of getting hurt in love, or that urge to just say, “I don’t want to figure out the political implications or the moral implications of my job, I’m just going to get on with my tiny patch”; those kinds of little urges we all recognise in ourselves—taking those and exaggerating them, and turning them into a kind of monstrous manifestation. The butler doesn’t look like a conventional monster, but I always thought that he was a kind of monster.

NG: I love the idea of Stevens as a monster!

KI: I’m reminded of something Lettie says in The Ocean at the End of the Lane: “Monsters come in all shapes and sizes. Some of them are things people are scared of. Some of them are things that look like things people used to be scared of a long time ago. Sometimes monsters are things people should be scared of, but they aren’t.” I thought that last category was really interesting. What are the monsters that stand for things that we should be afraid of but we aren’t?

NG: I think it’s very easy to not be afraid of slow things, and not be afraid of things that apparently have your best interests at heart, and sometimes not to be afraid of things that mask themselves in efficiency and humanity. I was reading the memoirs of Rudolf Höss, commandant of Auschwitz, and his letters home are filled with talking about how his men were working hard, who was doing well, how they got an extra trainload of people in, and: “By the way, give little Willy the present I sent and the chocolate, and I hope you enjoyed the schnapps.” And it was so horribly human. It is the monstrosity that waits there inside normality, that waits in humanity. I wish that all monsters could be serial killers, could be crazed, could be dangerous, but the problem is that they’re not. Some of them are, horrifyingly, people who in their own head have somehow got to the point where they think they’re doing a good job, doing the right thing. But they’re still monsters.

KI: You wonder about Boko Haram, these people who shoot buses full of children, who believe girls shouldn’t be educated and so on. Do they actually believe that they’re doing good?

NG: The tragedy for me of something even like 9/11 is that I do not believe that the people piloting those planes were going, “I am an evil person doing an evil thing.” I think they were going, “I am doing what God wants, I am doing God’s will; I am doing good, look at me striking against evil.”

KI: I wanted to ask you a bit more about ­stories being very long-lived beings. You’ve said that some stories actually adapt and survive as society changes around them.

NG: My favourite example of a story that mutates is “Cinderella”. The story may well have begun in China, where actually they care a lot more about foot size than they do in the west. But it reaches France, and you have a story about a girl whose dead mother gives her these fancy fur slippers, fur being “vair”, but somewhere in the retelling the V-A-I-R becomes V-E-R-R-E, and they become glass slippers. The homonym happens, and now you have glass slippers, which make no sense. You didn’t really have the technology in medieval France to make glass slippers; wearing them would be stupid, they would cut your feet, they would break. Yet, suddenly, you have an image that that story then coagulates around. And now “Cinderella” just spreads and spreads—it has a huge advantage over all the other stories about girls who are sort of dirty and sit by the fire and magic things happen to them. “Cinderella” is the one that survived.

KI: Do you think that if stories are left in the hands of professional storytelling institutions, like film studios and publishing houses, they are less likely to mutate in an honest way? Do you think the commercialisation of storytelling could actually be interfering in the natural development and growth of this kind of long-lived being?

NG: What a lovely idea! Where stories are concerned, I tend to be very Darwinian. Because I look at something like “Sleeping Beauty”. Disney retold “Sleeping Beauty”; one can assume that its “Sleeping Beauty” reached more people than any other version has. And yet, if people tell the story you won’t get the Disney version where she meets the prince that morning, you’ll get a tower of thorns growing up and a hundred years passing before a prince turns up. It feels like a much better version. I think that there’s definitely the battery farming of stories out there, but I don’t think they take over: they simply indulge our craving.

KI: Is fan fiction today an example of stories starting to mutate? Now you have this phenomenon, which involves both professional writers—P D James writing a sequel to Pride and Prejudice, or Sebastian Faulks writing another James Bond—and amateurs making up things around their favourite books, and writing prequels and sequels.

NG: It’s not a new phenomenon. I love the fact that, you know, in the early versions of King Lear, the story had a happy ending. Shakespeare turned it into a tragedy, and through the 18th and 19th centuries they kept trying to give it a happy ending again. But people kept going back to the one that Shakespeare created. You could definitely view Shakespeare as fan fiction, in his own way. I’ve only ever written, as far as I know, one book that did the thing that happens when people online get hold of it and start writing their own fiction, which was Good Omens, which I did with Terry Pratchett. It’s a 100,000-word book; there’s probably a million words of fiction out there by now, written by people who were inspired by characters in the book.

KI: What do you feel about that?

NG: Mostly I feel happy about it. But I think the happiest and proudest of people would have been, in those terms, the Stan Lees and the Jack Kirbys, the people who created characters in comics. Kirby was the artist, but also the creating, driving force behind the Fantastic Four, Iron Man, Captain America, the Hulk, the X-Men, in the early Sixties. These guys created characters about whom people are forever inventing, spinning off, and there’s something very wonderful about that.

KI: Yes, there is. I’m often asked what my attitude is to film, theatrical, radio adaptations of my novels. It’s very nice to have my story go out there, and if it’s in a different form, I want the thing to mutate slightly. I don’t want it to be an exact translation of my novel. I want it to be slightly different, because in a very vain kind of way, as a storyteller, I want my story to become like public property, so that it gains the status where people feel they can actually change it around and use it to express different things.

NG: Yes, the moment that you have a live actor portraying a character, something exciting is happening; it’s different, and if it’s really happening in front of you live, then, again, you’re seeing something that’s new. So I do love it when people grab my stuff and take it and do things with it. I love copyright—I love the fact that I can feed myself and feed my children with the stuff I make up. On the other hand, copyright length right now is life plus 75 years, and I don’t know that I want to be in control of what I’ve created for 75 years after I’ve died! I don’t know that I want to be feeding my great-grandchildren. I feel like they should be able to look after themselves, and not necessarily put limits on what I’ve created, if there’s something that would do better in the cultural dialogue. I loved Les Klinger’s legal case, establishing that the Conan Doyle Estate had basically been ­running a shakedown operation for the last 20, 30 years, where they’ve been getting people to pay money to license Sherlock Holmes when Holmes was out of copyright.

KI: I didn’t know about that, actually. Since Sherlock Holmes went out of copyright, certainly, he has started to mutate and evolve in a very energetic way. I don’t know if it would have been possible, for instance, to have the Cumberbatch modernised series, had it been under copyright. And Holmes is a very interesting example, I think, of a figure who’s mutated over the years and evolved. I think if you did a big study of Doctor Who, you’d see that the essential story has actually changed to serve the different climates of the times. It’s clear that the Daleks started off as Nazis and the Cybermen were communists. But my daughter was saying that, for their generation, the Cybermen represent the people being turned into mindless wage slaves in the 21st-century workplace. Now the fear of the communist takeover of the world has receded, the Cybermen can become almost the opposite—something that represents a unit of the rampant capitalist culture.

I wonder if Doctor Who will turn out to be one of these creatures who live for a long, long time, as a story that will be a hundred-year-old being, a 300-year-old being. I love this idea of yours of stories being long-lived beings because it seems to have implications for what our ambitions should be, as people who sit at home and write them.

NG: I know that when I create a story, I never know what’s going to work. Sometimes I will do something that I think was just a bit of fun, and people will love it and it catches fire, and sometimes I will work very hard on something that I think people will love, and it just fades: it never quite finds its people.

KI: Even if something doesn’t catch fire at the time, you may find it catches fire further down the line, in 20 years’ time, or 30 years’ time. That has happened, often.

NG: Exactly. There’s a beautiful essay by A A Milne where he says, “I want to draw your attention to a completely forgotten book that none of you have ever heard about that is one of the best books in the world, and it’s by Kenneth Grahame. And you’ve all heard of him, because he wrote Dream Days and The Golden Age”—two popular books—“but he also wrote a book called The Wind in the Willows, which none of you have heard of.”

KI: Aha. Stories are interesting in that way. They sometimes just emerge, after some mysterious kind of hibernation period. You can never tell what is going to be one of these long-lived creatures and what isn’t. It would be interesting to think, if stories are creatures, whether some of them are actually deceitful creatures. Some of them would be deeply sly and untrustworthy, and some of them would be very uplifting.

NG: There would definitely be bad ones. But how would we know? How would we ever find out?

“The Buried Giant” by Kazuo Ishiguro is published Faber & Faber. “Trigger Warning: Short Fictions and Disturbances” by Neil Gaiman is published by Headline.