It's classic Julian Fellowes fare: lemon-sucking snobs, sharp-elbowed upstarts, lusty servants and precarious fortunes.
Set in 1880s New York, when unimaginable wealth was pouring into the city and rattling the social structures, The Gilded Age is privilege porn extraordinaire. But what is it about the aristocratic classes that keeps drawing Baron Fellowes of West Stafford, to give him his proper title, back?
"I'd rather dispute that The Gilded Age falls squarely into that context because I think it's a different society," he says.
"The Gilded Age is about climbing ladders and getting to the top and all those other phrases. Of course, it deals with American class in a different way."
He reminds me of his work that broke away from upstairs-downstairs dynamics (writing the theatre adaptation of School of Rock, for example).
"I don't think it always has to be about class, but what I do find interesting is the influence of class on people's sense of self, whether they are diminished by it, encouraged by it, whether they have humility, false pride, or whether they're overconfident. Those people who never ask you a question because they think they're so grand. All of that fascinates me."
It's understandable if the 72-year-old is sensitive to suggestions that his new nine-part TV series follows a well-trodden Fellowesian formula.
Twenty years ago the landed gentry murder mystery Gosford Park won Fellowes a screenwriting Oscar; then Downton Abbey – which began in 2010 and ran for six seasons before shifting to the big screen – was a transatlantic triumph and is returning with a second film in March, but two shows in 2020, ITV's Belgravia and Netflix's The English Game, were less rapturously received.
Will The Gilded Age do better? After two years of social constraints viewers will surely lap up the opulence, lavish parties and dripping diamonds.
"Timing is very important but it's much easier to recognise it in retrospect, really," he says, speaking from his Chelsea pied-à-terre.
Fellowes and his wife, Emma Kitchener-Fellowes, the great-grandniece of the First World War general, share homes in Dorset and Mykonos, but when in London they live apart.
"I have this flat and she has a cottage just further down the Fulham Road, so that she can do all her charities, interviews and things, and I can work. I recommend it. It's only for two or three days a week, but it's great."
The series' casting is top-notch. In the old-money corner, there's acid-tongued Agnes van Rhijn (Christine Baranski of Mamma Mia! fame) and her meek sister, Ada Brook (Cynthia Nixon of Sex and the City fame) who take in their beautiful-but-broke niece, Marian Brook (Louisa Jacobson of being Meryl Streep's daughter fame).
In the arrivistes' corner, there is the railroad tycoon George Russell and his wife, Bertha, (played by Morgan Spector and Carrie Coon), who're fighting to get into high society.
Longing to belong is a theme; has Fellowes ever felt stuck on the outside, looking in? "Lots of times," he says.
"I grew up feeling I wasn't quite in the crowd because I had a brother, two-and-a-half years older than me, who was much more popular, and much better looking, much righter for the 1960s than I was."
Class is Fellowes' calling card, but Americans aren't as preoccupied with it as we are here. He argues that they obsess over success instead, which is better.
"It allows you to appreciate what's happening now and who people are right now. And not to be held by history sort of trailing at you. In that sense, I think society in America is invigorating; it's constantly reinventing itself."
Vast wealth breaks down social barriers in the US in a way that it often doesn't among blue-blooded Brits.
"When you are very successful as long as you're reasonably well mannered, and you're not offensive on the whole, the doors open because they just don't want to shut them if you've got $200 million," Fellowes says.
Whereas the British, he claims, are "odd" about success: "We're generous to people, as individuals, who reflect exactly our own values. But if there is any suspicion that they may not reflect our values, we then resent their success."
Fellowes is philosophical about success. He's come in for some scathing criticism, particularly around Downton Abbey, which a New York Times review witheringly described as a "warm bath of privilege".
"Those who prefer their ablutions minus the scum of entitlement can safely give this big-screen special a miss," it continued.
Fellowes is sanguine about such takedowns.
"I think for a variety of reasons, the kinds of literati disapprove of my success," he says. "There are certain shows [such as] Breaking Bad, which is a good show, or Succession, where they will go with that because they approve of it. But something like Downton they don't approve of, and its continuous success is an offensive thing."
One criticism levelled at Downton was the small number of black and ethnically diverse characters. Unsurprisingly, The Gilded Age, set 17 years after the abolition of slavery in America, has improved on this front.
Fellowes was inspired by Carla Peterson's book Black Gotham, which looked at a prosperous, bourgeois black population in 19th-century New York.
"I get worn out with always watching black characters as underdogs. And I think for black people to watch television and again and again and again they're underdogs, that must be very boring and tiresome," he says.
Fellowes also relied on the expertise of his black American series co-writer, Sonja Warfield (who has also published Get Your Butt Off My Couch, a self-help book for ditching deadbeat men).
He's interested in how the 1860s-1900 period spawned an all-powerful super-rich.
"These people weren't imitating Europeans," Fellowes says. "They made a new way of being rich and, to some extent, I think their way is the modern way."
The Vanderbilts and the Astors have modern equivalents, however he is sketchy on the facts: "Was it Steve Bezos and one of the others who had a rocket race to get to the moon? I thought, of course, it's just exactly like the Gilded Age when they were thundering down Fifth Avenue to prove whose carriage was faster."
In July 2021 Amazon billionaire Jeff Bezos was beaten into space by Richard Branson on his Virgin Galactic rocket.
Back in the UK, is this the final hurrah for Downton? "I've said goodbye to these characters so often. I thought the fifth series was the end, then I thought the sixth series was the end, then I thought the first film was the end. Woop, here we are again." Translation: let's not kill the golden goose before time.
Fellowes is also keen to get a mystery project with his 31-year-old son, Peregrine Kitchener-Fellowes, a film producer, off the ground. "I haven't been much help to him, which is quite impressive, I think. His first job was making coffee and parking cars on the set of Cinderella," he says. "And I think I was quite useful in that because I knew one of the producers but even then I didn't get him the job. I got him an interview."
However, Peregrine's cover as a regular flunkey on the 2015 Kenneth Branagh film was blown on day one. "Lily James [who played the title role] came out of the caravan on the first morning and said [Fellowes puts on a Violet Elizabeth Bott squeal], 'Peregrine, darling, what are you doing here?' "
In his 2002 Oscars speech, Fellowes described himself as "mean, moody and difficult" and it sounds as if he's obsessively focused when mid-project. "Working for an American company, you get about 47 times as many [script] notes. And that drives you mad, and you shout and throw things," he admits.
These days the workaholic grip is finally loosening, although he says that tireless ethic served him well over the years.
"I did get a lot done quite honestly. I did a lot of writing. Rather too much for some people, I'm sure."