Just going by numbers alone, it's undeniable that John Grisham is a statesman of American letters. Since the beginning of his career, his goal has been focused on output.

"One smart decision I made way back then was to hurry up and write," he said in an interview with NPR. He's published 49 books, and has sold more than 400 million copies, according to his publicist. He's been in the game for more than three decades now.

And in this tenured position in the world of books, he's adjacent to the existential crises facing books today. He's part of a big lawsuit against the artificial intelligence company OpenAI for copyright infringement (he said he's not allowed to comment on it). People often ask him about his stance on books being pulled from schools and library shelves (he said it is "ridiculous" but doesn't keep a close eye on the news).

Mostly, though, he'd rather be writing.

He's now out with his latest, The Exchange. It's a sequel to 1991's The Firm, which was the book that turned Grisham into a writing star. When I asked him why, after all this time, is he revisiting The Firm, he simply said: "Well, we're always trying to angle a way to sell more books."

The Firm was first published when Grisham was juggling working as a lawyer and being a member of the state legislature in Mississippi. He'd start his days early and write in the mornings. His first book, A Time To Kill, didn't do so well — at first, at least. Not until after he wrote his follow up, The Firm, which was an immediate success. "It was overnight," he said. "Terribly exciting."

The book is about a young hotshot lawyer named Mitch McDeere. He isn't a criminal defense attorney, or a white collar prosecutor, or anything exciting like that. He's a tax lawyer. And he gets recruited into a secret law firm in Memphis that, surprise, surprise, is doing shady business with shady people, and Mitch finds himself caught between the mob and the FBI.

The immediate bestseller was pulpy and breezy enough that it was prime material for a 1993 movie adaptation starring Tom Cruise. The movie was a hit, too, becoming the highest grossing R rated film that year. Suddenly, Grisham's work was a hot commodity in Hollywood: The Pelican Brief got turned into a movie. As did The Client. Then his first book, A Time To Kill.

"In the early 90s, things were really chaotic, but also a whole lot of fun. We were having a ball," he said of himself and his wife, Renee Grisham. But they also had their eyes towards the future — and on the cyclical nature of fame.

"We always said to each other, look, everything goes in cycles and nobody stays on top forever," he said. "Nothing is going to last forever. And so one of these days, this incredible journey is going to be over."

Even as the machinations of Hollywood taste changed, and options for his books kept going nowhere, Grisham kept hurrying up and writing. The Exchange takes place 15 years after The Firm. Mitch and his wife Abby live in New York City with their two children. It's a bigger globe trotting book — the main legal concern is over a fictional bridge in Libya that Col. Muammar Gaddafi wants built.

But before the main thrust of the narrative, there's a prelude of sorts that involves Mitch going back to Memphis to do some pro bono work involving a man on death row. Before he can even get started on the case, the man dies — supposedly by suicide. We never really come back to this storyline in the book but it serves multiple functions: It lets the reader revisit some of the story beats of the first book, but it also touches on the core of what drives so much of Grisham's work — injustice.

In 2006, Grisham wrote his first non-fiction book called The Innocent Man, about a wrongfully convicted man on death row. Since then, he's taken up the cause of wrongful convictions. He's on the boards The Innocence Project and Centurion Ministries, which helps get wrongfully convicted people out of prison. He is working on another book now, unsurprisingly. But it's a non-fiction collection about people spending decades in prison for someone else's crimes. "It happens all the time," he said.

Since the beginning of his career until now, not much has changed about his lifestyle, his writing process, or his demeanor. But what has shifted has been his faith in the jury system.

"We're supposed to trust the police and the prosecutors. We believe in those people, the judges. That's the system," he said. "And we want to believe that it always works and it doesn't.

Meghan Collins Sullivan edited the radio and digital versions of this story.