As the brassy, bitchy American heiress Martha Levinson on the coming third season of Downton Abbey, Shirley MacLaine defies British tradition and rattles the hallowed hallways.

The 78-year-old Academy Award winner is permed, primped, swathed in fur and armed with a collection of lethal zingers as Martha Levinson, the candid mother of Cora, Countess of Grantham. Levinson arrives from New York for a family wedding and creates a certain amount of chaos as she casts withering aspersions on the stuffy formalities of the English gentry.

Her two-episode appearance turns into a clash of wills—a delicious and sometimes malicious sparring match between MacLaine and Lady Violet, the acerbic Dowager Countess played by the formidable Maggie Smith.

The two legendary actresses forged a bond early in their respective careers, when they met backstage at the Academy Awards after MacLaine was passed over for an Oscar. Smith discovered her gorging on chocolate cake and muttering: “Hell, I don’t care. I don’t have to be thin anymore.”

Or at least “that’s how Maggie remembers it,” says MacLaine in a pre-Christmas phone interview from her home in Santa Fe, New Mexico. (She also spends time at her nearby ranch in Abiquiu and beachfront house in Malibu.)

One of MacLaine’s favorite bits of repartee took place off camera, when Smith removed her elaborate wig and MacLaine commented, “Maggie you have so much hair.”

“Yes,” quipped the jaunty septuagenarian. “I’ve been through a lot.”

MacLaine was not a devotee of the series when she was asked to join the ensemble, she says. Her hairdresser in Malibu filled her in, and after studying every episode she was “hooked, line and sinker,” and signed on.

“I loved the environment. It’s so classy and so well done. Every day stood out. The makeup, the sets, the wardrobe. It was extraordinarily artful and I thought ’Whoa, we’re making a painting here.’”

Downton Abbey, she said, stands out in her long and illustrious career because of “its universal appeal.”

“I can’t quite figure out why it is so successful in every culture on the planet. What is that all about? I think it’s about the structure of the timing. Something to do with the playing and it’s worth studying.”

She praised show creator Julian Fellowes, calling him “very British, obviously talented, with a sense a surprise about him because you can’t tell what he’s thinking or what’s coming next.”

MacLaine doesn’t even know if her character will return next season but said she’d happily reprise the role—if her busy schedule permits. At an age when most of her contemporaries are long retired, her professional life is booming.

"I love acting. I love the familiar environment. I love playing other people. I like it. I don't plan to quit," she says.

She recently completed a remake of The Secret Life of Walter Mitty with Ben Stiller, and is now shooting Elsa and Fred in New Orleans and Rome with former co-star and fellow Oscar winner Christopher Plummer, 83.

“It’s a love story between two old people,” she says. “We play old people and it’s very rewarding because there’s nothing else to go see these days if you are of a certain age.”

To play Elsa, she gained weight and walked in a slump in order to inhabit the character.

There is also her one-woman show, where she cruises into small towns across the country four of five times a year with old film clips and raps with her audience—unfiltered.”

I never know what I’m going to say and I make up a lot of different stuff,” she says, noting most questions from the audience deal with her best-selling books, rather than show business gossip.

Known for a strong interest in spiritualism, metaphysics and transcendental meditation she also discusses reincarnation, UFOs and what the world is coming to. Some of those topics are also addressed in her new book, still untitled, which she calls a compilation of everything in her head. “Movies, people, anything.”

Her proudest accomplishment beside her Oscar?

Receiving the American Film Institute Award earlier this year, making her and her younger brother Warren Beatty the only pair of siblings to achieve such recognition.

“That was very, very important to me,” she says. “You’re honored by your peers and the evening is all about your life and what you’ve done.”

Apparently the sole blip on MacLaine’s horizon is an upcoming memoir by her only child, daughter Sachi Parker, 56, due out next year.

According to the National Enquirer, the sarcastic tell-all, entitled ”Lucky Me- My Life with-And Without—My Mom Shirley MacLaine,” paints a potentially disturbing “Mommie Dearest” picture.

“I don’t know. I have no idea. I don’t know anything about it,” MacLaine says when asked about the book, though she does say she is in contact with Sachi.

When pressed further, she dismisses the subject: “Look, it’s mother-daughter stuff.”

Her life, she continues, was, is and will go on as a combination of comedy and drama. “Everything that happened was supposed to be at the time, and there is no point in making any kind of judgments.”