"Being on 'Masterpiece' is like telling a Jewish mother that you're going to be a doctor," Piven said. "Basically, it's like I've made it."
"Selfridge" is the fact-based story of Harry Gordon Selfridge, the man who made Marshall Fields a huge success in Chicago and then traveled to London, where he set the retail world and England on their ear with his own department store.
It's a costume drama but it's anything but staid. Which caught the attention of Piven, who said he had no plans to do another TV series on either side of the Atlantic.
"As I was reading it, I was willing my beard to grow because I knew that there's no way that I could say no," Piven said. "I hadn't even finished it when I knew that I would jump right into this."
He wasn't the only one surprised by the story. Producer/writer Andrew Davies, whose credits include "House of Cards," "Little Dorrit," "Bleak House" and "Bridget Jones' Diary," said he was not interested when the idea of adapting Lindy Woodhead's book Shopping, Seduction & Mr Selfridge was pitched to him.
"It's all about shopping," he said. "I'm a guy. I don't do shopping."
But he agreed to read the book and was "completely gripped by the story, because it seemed to me like a kind of tale about the American dream lived out in London. A guy who wanted to have it all. He wanted the impossible."
Selfridge wanted a home, a family, success and lots of women.
"He was an exceptionally active man with the ladies," Davies said. "He loved his wife, but he couldn't resist pretty women. And he had, in fact, scores of girlfriends."
In the eight-part series, Selfridge's mistress, Ellen Love (Zoe Tapper), is "kind of amalgam of one or two or three or four" of those women.
"Selfridge" is not just about the title character's love life. It's about a clash of cultures. About a brash American crashing into a British culture that was undergoing considerable change.
"He was like a whirlwind, and he ruffled feathers," said Tapper.
"And he didn't know the English rules, so he didn't play by the English rules," added Frances O'Connor, who plays Harry's wife, Rose.
Before his store opened in 1909, people didn't shop for pleasure. The rich sent out for what they needed. Women were accompanied by chaperones when they went out.
"He actually transformed shopping," Piven said.
"Actually going shopping somewhere like Selfridges was the first time that women were allowed the freedom to go there alone," Tapper said. "It sounds quite strange now, but it was quite an emancipating scenario for them."
Selfridge is the guy who came up with the "only [blank] more shopping days until Christmas" idea. And he may have coined the phrase "The customer is always right."
He was a larger-than-life personality, which makes for a very entertaining TV series.
"He loved P.T. Barnum, and he thought of himself as a performer," Piven said. "And the store was his theater."
"Mr. Selfridge" premieres Sunday at 8 p.m. on PBS/Channel 7. The eight-part series continues through Sunday, May 19.