Ryan O’Neal, in those days, was still one of Hollywood’s favorite bad boys, a rake with sandy hair and a Pepsodent smile. He had already dispatched the hearts of Ursula Andress, Bianca Jagger, two wives, and a host of others. And as he pulled up to the entrance of the Beverly Hills Hotel on that day in 1979, driving a beige Rolls and wearing a Hawaiian shirt, he was soon to do the same to Margaret Trudeau, the wispy, glamorous wife of the prime minister of Canada. Maggie—as her friends knew her—would later note that theirs was “one of the shortest-lived, most exciting and absurd” affairs of her life; the 38-year-old O’Neal was “shallow” and represented “everything that was wrong about the way I lived.”

And, boy, how Margaret Trudeau had lived. By the late 1970s she was an international sensation, the Holly Golightly of the Mounties, the wayward wife who had left Canada’s dashing, intellectual prime minister, Pierre, and their three young sons (the eldest, Justin, became prime minister in 2015) to pursue a life of glitz and unbridled hedonism that was splashed on the pages of every international tabloid. She had met O’Neal at Studio 54, where she was a regular (“He was sort of like Cary Grant and Peter Lawford—lanky and tall and elegant, just perfect lines everywhere,” she says today), and where she once memorably sat on a patron’s birthday cake. A photo of her kicking up her heels on the 54 dance floor—the same night in 1979 that her then husband lost re-election—was zapped all over the world, confirmative evidence of her status as the gold standard in reckless bohemian chic.

As most of O’Neal’s conquests did, Margaret enjoyed frisky fun with him, tumbling for his mix of boy-next-door charm and a touch of menace. (O’Neal declined to comment for this article.) Until the day she taped an episode of The Mike Douglas Show and then went to his house to see him, only to be told he couldn’t let her in because his son was at home. Piqued and undaunted, she hiked up her tight leather skirt and scaled the high wall surrounding O’Neal’s mansion, teetering on black suede pumps as her driver looked on, suitably agog. O’Neal had been appalled, amused, and impressed, but not enough to hang around for more: things quickly flamed out. So Margaret Trudeau did the only thing she could think of, which was to stop for Japanese takeout, then have the driver pull over on Sunset Boulevard so she could toss the entire meal at a billboard for The Main Event, O’Neal’s new movie.

By the late 70s she was an international sensation, the Holly Golightly of the Mounties.

I remind her of this story one night as we sit in the back of a car, on the outskirts of Toronto. It’s not a funny memory. “Oh, the madness . . . ,” she says, trailing off, looking out the window. She’s come to terms with all of this, with her torrid past and its resulting infamy, and with her serenity about it all, which seems genuine and hard-won. But despite her fortitude, she cannot completely vanquish regret, having lived a big, wild, public life. “You look back and you wonder, How could I have? And yet you know you were trapped in the reality of mental illness.”

Margaret doesn’t tell the O’Neal story in the speeches she now makes. But she tells others, many just as shocking and scandalous and embarrassing. She’d rather not, of course, but she knows she has to. Because she has to be authentic, she has to tell the truth, she has to get people to listen, to understand that what happened to her is happening every day to other people whose foibles never make it into the Daily Mail. You can call it a crusade, or, if you’re a cynic, you can call it Margaret Trudeau giving a narrative to her past bad behavior under the guise of being a mental-health advocate. She doesn’t particularly care. She knows that she hasn’t always done the right thing but that she’s doing the right thing now.