The comedic set-up could be a movie. One day a beloved Hollywood megastar e-mails an eccentric British writer seeking to collaborate on a tie-in novel based on an ultraviolent comic book.

The exuberant A-lister envelops the mild-mannered, high-minded homme de lettres. Los Angeles collides with Kilburn. American trash entertainment swallows subtle British intellect whole. Fish-out-of-water confusion, hilarity and (presumably) a product of unparalleled vulgarity follows.

Except The Book of Elsewhere, a novel brought to you by Keanu Reeves and China Miéville, is nothing like that. Yes, one day in 2021 Reeves, the star of The Matrix and John Wick, did e-mail the acclaimed author Miéville to ask him if he wanted to write a novel that takes place in his cartoon world. There the similarities with my set-up end.

For one thing, The Book of Elsewhere is a surprisingly, even rattlingly good read about a warrior on an ultraviolent millennia-long quest to discover the key to his immortality, and maybe free himself from it. The novel is a spin-off from Reeves’s BRZRKR universe — everyone in Hollywood has their own universe now — a 12-issue comic book series that he began writing in 2021. Discussions for an adaptation, perhaps with Netflix, are in progress. Twenty-five years on from The Matrix, Reeves is still fascinated by science fiction, as this project demonstrates. “It’s a Trojan horse of a genre,” he says.

The Book of Elsewhere is a surprisingly, even rattlingly good read about a warrior on an ultraviolent millennia-long quest to discover the key to his immortality.

It becomes clear when I speak to Reeves and Miéville that this is not a case of Hollywood giving orders to a lowly scribe. If anything the power dynamic flowed in the other direction.

“He was, like, ‘Yeah, I like you, Keanu, and this idea seems intriguing,’” Reeves says of his initial approach to Miéville three years ago. “‘But’ — and I found this f***ing awesome — ‘by the way I need six more months to work on a different story for myself.’”

“I didn’t quite say it in such an offhand manner,” Miéville says, chuckling. The British author, bald, bespectacled and pristine-looking at 51, is speaking from a gloomy room in Berlin. Reeves, 59, who talks in breezy, sweary, woo-woo Californian, joins from a West Hollywood conservatory charged with Pacific sunshine.

Mysteriously, Reeves’s black hair is standing on end, like that of an electrified cartoon character. Together they make a flirtatious odd couple: Reeves boyish and excitable, Miéville academic and droll. Yet there is a real equivalence: Reeves is Hollywood royalty, Miéville is one of the finest writers in his field, a winner of the Arthur C Clarke and Hugo awards — the fantasy equivalent of cleaning up at the Oscars.

“He said it relatively stridently,” Reeves protests as Miéville laughs. “If you don’t accept these terms, then ‘It was nice to meet you.’” You get the sense that not many people ever say no to Reeves, and that he loved Miéville all the more for it.

This is not a case of Hollywood giving orders to a lowly scribe.

“That to me was, like, ‘F*** yeah,’” Reeves says. “It was like an artist saying, ‘I want to work with you, but I’m [busy] creating something.’” Reeves, a long-term fan of Miéville’s work, waited the six months.

Miéville had another book — a marathon 20-year project he terrifyingly refers to as his “Matterhorn” and “white whale” — to finish. It’s a novel that will be out next year. His previous genre-bending books include The City & The City, Embassytown, and Perdido Street Station. The Book of Elsewhere — a commission that “delighted” and “surprised” him — is Miéville’s first piece of fiction in almost ten years.

There has been no drop in the quality of Miéville’s writing. A blood-spattered, era-spanning action thriller, The Book of Elsewhere manages to lift and twist its unbelievably sanguinary source material into a meditation on the cyclical nature of violence.

“Something’s being worked out,” Reeves says of the novel’s more bloodthirsty scenes. “I think there’s something about it [violence] being in our stories that helps us deal with it.” What Reeves jokingly calls a “f***ing comic book” has been transformed by Miéville into quasi-philosophy.

We follow B, an ancient super-soldier “nearly 20 times older than the oldest pyramid” in search of an end to his immortality. B doesn’t want to die, but he would like to have the option to do so. For that reason he finds himself working for the US government. He does perilous black ops work for the military while they study him to see if his super-strength is replicable and find a cure for his condition.

Both men are fascinated by the fictional possibilities of an immortal character. Like a Hollywood A-lister, B is embedded in the world yet distant from it. Reeves understands mortality. He lost a daughter to a stillbirth in 2000. Her mother, the actress Jennifer Syme, died in 2001 after a car accident. She was 28. Melancholy, whether in The Matrix or John Wick, is often the key to Reeves’s performances. So too in this novel, which is about “the toll of immortality on love and watching people pass. There’s a lot about grief.”

Like a Hollywood A-lister, B is embedded in the world yet distant from it.

The Book of Elsewhere combines what Reeves calls the “pulpy” elements with these more heightened emotions. “The pulpy thing helps the medicine go down,” he says. You sense that the emotional temperature of the novel was set by him, then interpreted by Miéville.

The result in The Book of Elsewhere is a coolly melancholic tone that has much in common with Reeves’s best film roles. B is “seeking his humanity” and “understanding of the self”, Reeves says. “As we all know in our own lives, that’s not always so easy. And then you add immortality … ”

B was lurking in Reeves’s mind “for at least eight years” as a “character cursed with violence”. In the comics and The Book of Elsewhere B is a mirror physical image of the action titan: tall, lean and grimacing beneath a fringe of black hair. Reeves definitely isn’t immortal, however. “No, I’m turning 60 and feeling every second of it,” he says with a sigh. “I’m just glad to be here.”

The Book of Elsewhere was “joyful” to write, Miéville says. After laying down the structure and the non-negotiable elements of the BRZRKR lore dreamed up by Reeves, Miéville was free to do whatever he wanted with the characters. “There’s a certain kind of liberation in playing with someone else’s toys.”

The “Matterhorn” novel that he finished before this project will weigh in at about a thousand pages; he sounds relieved that it’s over at last. Reeves has the expectant grin of a soon-to-be-satiated fan on his face when Miéville talks about it. The Book of Elsewhere was delivered in four drafts after what sounds like a much more painless process.

There was only one real problem that crept up during the back and forth between the two men: a software issue. “I had no idea how to use Microsoft Word,” Reeves recalls. Miéville calmly showed Reeves how that worked, then taught him a few things about novels too.

Will Lloyd is a news reporter for The Sunday Times. He has written about culture and politics, and was previously a commissioning editor and writer at The New Statesman