Fantasy author Neil Gaiman has been talking about managing the Amazon / BBC production of Good Omens for months now. Even so, he still gets emotional about Terry Pratchett, his co-author on the 1990 novel that the series adapts. “All I wanted to do was to make something Terry would have liked,” Gaiman says. “That was the only rule.”

Gaiman is no stranger to working in television. Many of his comics and novels have been adapted for the screen, from the 1996 BBC miniseries Neverwhere to the Starz adaptation of his novel American Gods, which he produced. But Good Omens, which he scripted and produced, represented a new level of commitment for him. As the showrunner, he personally oversaw every step of production, per Pratchett’s dying wish that he make sure an adaptation was done right. Good Omens is Gaiman’s extremely faithful adaptation of the apocalyptic tale he and Pratchett wrote together. It follows the angel Aziraphale (Michael Sheen) and the demon Crowley (David Tennant) as they attempt to prevent the end times.

Directed entirely by Douglas Mackinnon (Doctor Who, Outlander), the series has an all-star cast largely from Gaiman’s personal contacts, including Jon Hamm, Josie Lawrence, Adria Arjona, Michael McKean, Jack Whitehall, Miranda Richardson, and Nick Offerman. Many of them, Gaiman says, were fans of the novel. Together, they ultimately just wanted to respect Pratchett’s wishes for a good adaptation.

The interview has been edited for clarity and length.

What was your approach in figuring out what the story needed to work as a miniseries?

Picking up a copy of the book that’s about 360 pages long in this edition and putting in a Post-it note every 60 pages. That gives us six episodes. And then looking at each 60-page chunk, looking at episode 3, going, “That’s weird, Crowley and Aziraphale aren’t in this one. Why don’t I just do a sort of pre-credit sequence — just the 6,000 years of human history where you get to find out how they got where they were?”

Get to episode 6, go, “That’s interesting, if I shoot it like this, I’m going to run out of plot halfway through the episode, and then it’s going to get really dull. I’m going to have to fix that, but I don’t know how yet. I’ll figure it out. I do know the angels are in it. And I do know hell is in it. Now I’m going to start, and let’s see where that takes us.” And that really was the process.

“[Terry] died, and I went to the funeral, flew home, landed, and started writing episode 1, in a world in which nothing seemed very funny.”

Terry was in a coma, I think, at the point when I was doing that. I got a letter from him, saying, “Please do this for me.” And then he died, and I flew to England. I did a 48-hour round trip, went to the funeral, flew home, landed, and started writing episode 1, in a world in which nothing seemed very funny. That was the process. Write it script by script, just try to envision the television series that I would like to see.

We had talked, Terry and I, a lot about the angels. The angels actually showed up in a first draft of the Good Omens film script we did. For some reason, the studio couldn’t come to terms with the idea of Aziraphale owning a bookshop, so he had to work in the British Museum. So there was a scene where he was pursued through the British Museum by angels flicking on their halos then throwing them like killer Frisbees.

It was just that thing of going, “Okay, we need angels in here to balance everything out. We need a few more. We’ve got a couple of demons.” I was like, “Okay, let’s see heaven, let’s see hell.” That all really just grew organically. And by the time I got to episode 6, all of the solutions to my clock problems were just waiting for me in there.

How much of Gabriel’s persona and character were on the page before Jon Hamm came in?

All of it. I went, “Okay, I need somebody who has to be bigger, better-looking, and better-dressed than Aziraphale. They need to be able to deliver these lines with absolute certainty of their own rightness. And you have to want to hit them in the face all the time.” And so I wrote an email to Jon Hamm and said, “Jon, you told me once that Good Omens was one of your favorite books 20 years ago. Would you like to be the angel Gabriel? This is what he is. And, by the way, he’s not in the book.” And I got a one-word email back, which just said, “Yes.” So now I had a Jon Hamm.

That reveals a lot about the book’s huge fan base.

Which is why Michael [Sheen] did it. And Sister Mary, Nina Sosanya. She read it first when she was 15, and she’s read it every year since, and she loves it. She was the first actor we got, who crystallized for me, “Okay, this is the kind of performance that we need.” Up until that point, we’d been auditioning nuns, and they all knew the thing was funny, so we were getting funny performances from them. And it was like, “No, do what Nina’s doing, where she plays it absolutely and utterly straight, and it’s hilarious.”

Did you have any brain trust or producers you consulted about the changes you were making to the story?

The most important one was Rob Wilkins, who is Terry Pratchett’s representative on Earth. I remember the point where I figured out what I was going to do in episode 6, how I was going to get a plot that ran all the way through the end. And the idea that I was going to start episode 6 with Crowley’s trial. I remember texting Rob, “Oh, this is so fucking clever.”

When we were working on the scripts, [we were working exclusively] with the BBC. The BBC didn’t give the kind of notes you might expect from a studio, I think partly because they knew it had gone so far beyond their budget from like halfway through episode 1. They were like, “We’ll just let him write.” And then we got to take those scripts to Amazon [which co-produced the series], and they’re like, “Oh, we love this. Okay.” So it was very simple.

But there were surprises all the way through the very, very end. Some of it was the show wasn’t done until every bit of it was done, which included the graphics, the voices, the last VFX, the grading, the coloring. Suddenly, it’s like, “Oh, that’s what we made.”

Do you feel pressure from knowing this has to be the definitive best adaptation it could be?

No. All I wanted to do was to make something Terry would have liked. It wasn’t like, “Make the best thing.” I like to think of things like this almost as school plays. “Here’s our school play of Good Omens. We’ve got Michael and David. We have Frances McDormand and Benedict Cumberbatch, Nick Offerman, Nina Sosanya, Miranda Richardson, Adria Arjona, Jack Whitehall, all of these great people in it. But you can put on your school play next year.”

How does it feel to know your version is out there?

Wonderful, really wonderful. Mostly because I feel like I’ve been… it’s like in a cartoon, where somebody goes into the laboratory, and then you just see the “keep out” sign, and you hear hammering for a while, and suddenly the door opens, and there is the robot or whatever they’ve been making. And now I’m letting everybody see the robot. And that is so exciting. This is four years of my life, and I loved it, and I’m really looking forward to it being done.

From everything you’ve said publicly over the years, it seems like this was a really great experience you look forward to never having again.

Yeah, I was not put on this planet to have to argue with someone about fucking budgets.

The things you do for Terry.

Yeah, there was an awful lot of “Great, you lumbered me with this, and then you buggered off.”

Probably the biggest reason I’m thrilled to have done it is a kind of proof of concept. Over the years, I’ve made lots of things, and they’re all a bit odd, but I’ve always loved that. You look at Anansi Boys, Coraline, The Ocean at The End of the Lane, they’re not like other things. Sandman, it’s not like other things.

A lot of them have been adapted, some of them adapted really well, and a lot of them have failed to actually go to the screen. But there’s definitely a level on which I wind up feeling like I can point at something and go, “I think it would be really good if you did that thing that’s in the book because I think it will work.”

The lovely thing about Good Omens [the miniseries] is that it’s still Good Omens. If you loved the book, this is that thing that you loved. And I will make you fall in love even more with Sergeant Shadwell. I will make you fall even more in love with Newt than you thought you could, I hope. It does demonstrate that I do kind of know what I’m talking about, which is a nice thing to know.

The adaptation process must feel like watching something you’ve said translated into a different language.

There’s also just the feeling of wanting to demonstrate to people that this stuff actually does work as written. It doesn’t have to be fixed. The number of adaptations of Sandman I have read over the years — mostly, I watch people trying desperately to fix the things they think are broken in it. I look at it and I go, “Actually, this works, and you’d be much better off if you just did the thing I did. Then it would work.”

So with Good Omens, I feel like what I got to do was put the thing I made with Terry on the screen and then buttress it. What I added isn’t completely different from the original. It’s not out of left field.

The biggest changes from the book to the show all seem to reflect it becoming the story of two friends.

It’s true. Although, if you told me that when I sat down to write it, I might have been quite surprised. It became very apparent when I was writing that the song “A Nightingale Sang in Berkeley Square” is a better place to end the television show than [the place where the book ended].

You had Tori Amos record an original cover of that song, which is an old standard. What’s its significance here?

It’s an English song, although I believe it was written before the war, by an expat from France. [Note: The song was written in 1939, with lyrics by Eric Maschwitz and music by Manning Sherwin.] And it just lists the strange things that happen one night that have never happened before.

The book has the line “for the first time ever, a nightingale sang in Berkeley Square.” That was mine because I liked that idea that, for once, a nightingale actually did sing in Berkeley Square. The whole point of [the song] is, there are all these things that never happened except this one time… and there’s a lyric about “there were angels dining at the Ritz.”

And then while writing, I spent probably four days listening to versions of “A Nightingale Sang in Berkeley Square.” Every version on Spotify, every version on YouTube, going, “There’s a version I have in my head that I need to finish with. It’s got to be dinner piano, and it has to go into somebody singing it and breaking your heart.”

I listened to version after version, and [the one I envisioned] didn’t exist. So I reached out to Tori Amos [a longtime friend] and said, “Please come into the cutting room, I want to show you stuff.” And I showed her what we were doing and showed her the end, and I just said, “Look, will you do this thing? Going from dinner piano, we’ll bring in some strings, but I want you to sing the song.”

“I think it will be much harder for a future showrunner to bullshit me.”

All I requested of her was just the first verse or two, and she actually does three verses and a little wrap-up. It seems to be the only time I’ve ever run into people that say they’ve sat and watched the whole of the credits, just because they wanted to listen to Tori singing and find out how it ended.

It’s a nice cherry on this sundae because so much of Good Omens is built around people you already knew.

These are my friends. Like I said, it’s like a school play.

You’ve said you never want to be a showrunner again, but what about this experience do you plan to use in the future?

I think it will be much harder for a future showrunner to bullshit me. I think there are definitely places where I will be firmer on things where I wouldn’t have necessarily been in the past. I’m still going to be writing scripts, I’m still going to be making things. I just don’t ever want to showrun a six-episode thing again.