At New York Comic Con this weekend, Amazon released the first look at its upcoming miniseries, Good Omens, based on the classic fantasy novel. At a press event, co-creator Neil Gaiman and members of the cast explained their approach to adapting the book for television.

The comedic fantasy novel was a collaboration between Neil Gaiman and the late Terry Pratchett, in which Aziraphale, an angel played by Michael Sheen, and Crowley, a demon played by David Tennant, must collaborate to stop the coming end times. The two have become unlikely friends in the last 6,000 years, and together they’ve come to like living on Earth, and don’t want to see it end. The trailer introduces us to both creatures as Crowley reaches out to Aziraphale to tell him that the world is coming to an end. It goes on to detail their long years of friendship as they meet run into one another over the years; from the looks of it, the series will have a real buddy-comedy feel as the two team up to stave off armageddon.

Speaking to The Verge at New York Comic Con, Gaiman reflected on developing the show without Pratchett, who died in 2015 due to complications from Alzheimer’s Disease. He explained that the two had discussed adapting the series (there had been a film with Robin Williams and Johnny Depp planned at one point), and they had agreed that, like the book, working on an adaptation would be a collaborative project. “We only did things together, or not at all,” he said. Before his death, however, Pratchett told Gaiman that he had to go forward without him. “I came back from his funeral and started writing the first episode of Good Omens,” he said, “and tried to convince myself that it was funny.”

“I was writing them for a very specific audience, Terry Pratchett. That was my standard.”

Without Pratchett to fill out the duo’s writing process, Gaiman says he had to find workarounds. “There would be two different phenomena going on,” he says. “One was, if I got stuck during the writing process, what I’d always done before on Good Omens, was to call Terry.” Gaiman would “either send him what [I’d] done so far, and he looks at it and carries on writing it, or he phones you up and says ‘the answer, grasshopper, is in the way you ask the question!’ [I’d] then go, ‘Terry, don’t be irritating, tell me what you think.’” With the series, though, he couldn’t do either of those, but imagined writing for Pratchett anyway. “When you write a book or TV show, you have an imaginary audience in your head,” he says. “When I wrote my bits of Good Omens, the novel, I was writing them for a very specific audience: Terry Pratchett. That was my standard [for the series, as well].”

Series director Douglas Mackinnon noted that while he had never met Pratchett, the author’s presence was there on the set, and that they worked to honor his sense of humor, but also to ensure that the series could stand on its own, rather than being a strict retelling of the original novel. Sheen notes that Mackinnon was protective of the book, with a well-thumbed copy close at hand to refer to as needed. But “at a certain point, you have to let go of what it was before,” Sheen says, “and then, hopefully, if someone comes and reminds you, ‘That’s just like that bit in the book,’ you go, ‘Thank god for that, I must be doing it right.’”

“I think once we started shooting, I put the book down, actually,” Tennant chimes in. “In a way, it then becomes its own beast, and you’re playing each scene as it comes up. There has to come a point where you have to go ‘Well, now it’s this, we’ve made a decision, and that’s the story we’re telling.”

“That’s where having Neil [Gaiman] on set really helps,” Sheen adds, “because you know you can’t veer off too much, [and] you’re sort of getting [his] seal of approval every day.”

Good Omens will begin streaming on Amazon Prime in 2019.