IT'S 20 years since Edward Norton first read Motherless Brooklyn, about a detective who has Tourette's disorder.
Bringing the book (by New Yorker Jonathan Lethem) to life has been a passion project for the Boston-born star ever since. Part of the appeal was that protagonist Lionel Essrog is "not your traditional kind of tough guy detective".
"He is sort of the opposite of that," suggests 50-year-old Norton, known for films such as Fight Club, Birdman and American History X.
"He's tough and relentless, but people view him in a diminished light. They assume that he's not as smart as he is because of his condition. But that's what makes it fun, I think – the idea that you're rooting for the guy that other people aren't seeing for who he really is."
We learn Lionel was an orphaned kid growing up on the mean streets of Brooklyn when he was taken under the wing of Frank Minna, a private detective (Bruce Willis).
His condition means he twitches and shouts a lot; in an early voiceover, he says, "It makes me look like a damn freak show".
But the lonely figure doesn't let his behaviour stand in the way of his job. In fact, his obsessive personality, photographic memory and powers of pattern recognition make him a force to be reckoned with.
"There was a very positive side to Lionel's obsessive personality, which is that he holds information, as he says, like 'glass in the brain'," explains Norton, who's married to Canadian film producer Shauna Robertson.
"Lionel can't let things lie, he can't not pull on a thread, he can't stop thinking about things that haven't yet fit together. So, as a detective, he has a relentless compulsion to figure out what's really going on around him that I found exciting and moving."
When tragedy hits the agency he works at, Lionel takes it upon himself to find out why, resulting in a deep dive into troubling political issues across the city.
Along the way, he meets alluring community activist Laura (Gugu Mbatha-Raw), and Norton depicts Lionel's vulnerability with her just beautifully.
But when he uncovers closely guarded secrets about ambitious developer Moses Randolph (Alec Baldwin) – the most powerful man in the city – Laura is left in serious danger.
During the adaptation process, Norton made the decision to scrap the original late 1990s setting in favour of the 1950s.
"I've long been interested in what was happening behind the scenes in the development of New York in the late 1950s, when the old New York became the modern city," says the amiable star.
"It felt like a very charged place to put Lionel. Thankfully, Jonathan is as passionate a student of New York as I am, and he completely understood what I hoped to do, so I couldn't have been luckier."
Motherless Brooklyn is a timely crime thriller, with identity, corruption and politics at the heart of it.
In terms of how else the project changed over the years, did Norton try and make the script more relevant to audiences today?
"I think, in a way, what happened in the world around it made it feel even more resonant, because of some of the themes that are in it," he muses.
"There's ideas in it about the danger of people having power in a shadowy way. When we can't see what's really going on, when we can't see how people are manipulating us, corruption and greed and things like that can do real damage."
I prod him to elaborate, suggesting he's referring to Donald Trump being elected as president.
"Yeah," he responds hesitantly. "Well, I think, post-2016 [Trump's election year], there were some aspects of this story that took on a special resonance."
Discussing the adaptation process further, Norton confides it took a while to get the script right.
His own reservations got in the way too; a part of him was happy to keep putting the mammoth project off.
"I would get close to where I thought, 'Ah maybe I'll do this now' and then I would get an offer to get some cool film like Wes Anderson or Birdman or something like that.
"And, you know, you keep going, 'I'll do this after I've done that', because it's easier."
Arguably, the film's greatest strength is Norton's meticulous and striking performance as Lionel. Did he have any fears about portraying someone with Tourette's?
"Not fears... I think, fundamentally, the story actually focuses on his emotional life as a person; it lets you into his world behind the condition.
"And also in many ways it's about how, like all of us, he's got to ultimately grow up and look beyond his own personal issues, and figure out that being heroic means kinda caring about other people too, not just worrying about his own problems.
"The best way to portray anybody is to deal with their complex, full humanity, not to reduce them to that condition."
Lionel is certainly a character Norton found memorable from the very first page of Lethem's novel.
"He's dysfunctional in funny ways but also that are a little bit painful at times. He's tough, and a Brooklyn orphan street kid, but he's also sensitive and lonely. He trips himself up, but he's also got talents, and it's all that complexity."
"Ultimately," the film-maker concludes, "I think it's that I love an underdog story. And you really root for him as the story goes on."
:: Motherless Brooklyn is in cinemas now.
