Deborah Mitford, the last of the "Mitford Girls," died this week in England at the age of 94. She and her five sisters, Nancy, Pamela, Diana, Unity and Jessica (called Decca), were the Middletons of their day. That is, if Kate had literary talent, and was ever called upon to utter a political opinion. And if Pippa married a fascist.

Deborah was, by marriage, the Duchess of Devonshire. She was not the quietest of the Mitfords; that would be Pamela, a woman who in adult life mostly farmed and was much less of a gadabout than the rest. Deborah wrote books, as Nancy and Decca did, though they were mostly about Chatsworth House, the family seat (and which Barry Lyndon fans will recognize as the house where it was filmed). Her Mitfordian-ness comes out more clearly in her letters to her sisters, and in the sort of laconic high-mindedness she displayed in television interviews late in life, as she does in this BBC documentary about the debutantes of the late 1930s.

As the baby Debo was picked on, particularly by the brilliant eldest, Nancy. Nancy was honing the biting satirical wit which would become the trademark of her novels, like The Pursuit of Love and Love in a Cold Climate, a gimlet-eyed take on the English country romance. "Debo," as the youngest was called, would write later that Nancy "once upset us by saying to Unity, Decca and me, 'Do you realize that the middle of your names are nit, sick and bore?'"

Debo claimed not to resent such insults. This sort of repartee was the preferred mode of communication in the Mitford's household. And besides, she'd tell an interviewer in 2010,

I should think the social services would be called in now... But I adored [Nancy]. I used to sit on her bed for hours being mentally tortured. I would be in tears succeeded by roars of laughter. She was so funny, you see, and people don't seem to be quite so funny any more.

Few people were probably ever as funny as Nancy Mitford, to be fair. But Debo was not wrong to observe that some kind of era has passed. There was a certain kind of lacerating intelligence intrinsic to Mitford wit; now someone might hear these jokes and call them cruel, and they were cruel, because sharpness was a quality the Mitford sisters prized among themselves. They loved each other dearly but also fought each other with every scrap of emotional energy that implies.

And their sharpness didn't always work out well for them.

The key example: You cannot write about the Mitford sisters without mentioning Hitler. First there is the matter of Unity, who became intrigued by fascism at a young age. Diana would also divorce a baron to marry the head of the British Union of Fascists (in Goebbels' living room) but she still could not match the dramatics with which Unity lived her extreme-right-wing beliefs.

Unity had an obsessive turn of mind overall, was a natural fanatic. As her biographers recount, by 1935 21-year-old Unity was trying to stalk Hitler in the papers, figuring out where he'd be so she could lurk nearby to meet him. She figured out his favourite restaurant, and staked it out. The scheme worked, as detailed in Mary S. Lovell's The Sisters: The Saga of the Mitford Family:

When he appeared she made small attempts to be noticed, such as dropping her book. Eventually this paid off. Hitler became used to seeing the tall, Nordic-looking girl — often alone — sitting in the same seat every time he visited the Osteria, and saw that her attention was fixed constantly on him. To her huge delight he began to nod to her sometimes as he passed her table. Eventually he became curious enough, exactly as she'd hoped, to enquire of the restaurant owner, Herr Deutelmoser, who she was.

Once they started talking it appears they rarely stopped. Per Lovell, Unity's diary records over a hundred conversations with Hitler from 1935 through 1939. Over the course of their friendship he did all the usual nice-Hitler things like gift her a pistol (apparently Hitler was into women's self-defense) and get her and Diana seats next to Eva Braun at the 1935 Nuremberg rally and take Unity to a great many Wagner operas.

There were always questions about whether the relationship was sexual but Unity's sisters denied it late in life — you can watch Debo emphatically dismiss the idea on television four years ago here. Still they had pet names for each other: Wolf for Hitler, Kind (child) for Unity. Whatever her romantic intentions, largely it seems that Unity saw herself as building an alliance between Nazi Germany and the Brits, not that she seems to have gotten very far.

By 1938 Unity was finding that the atmosphere in England was inhospitable to her fascist beliefs; at a rally in Hyde Park someone tore a swastika badge from her shirt and she was kicked and mauled by the crowd. She remained defiant in her beliefs right up to the day Britain declared war on Germany. After learning the news at the British consulate, she went home, wrote a suicide note, made some personal arrangements, drove to a park, and shot herself in the head.

Unity survived the suicide attempt. She was taken to a hospital in a coma. Hitler visited her there. When she regained consciousness, Unity told him she wanted to go home to England, and eventually he managed to get her to Switzerland. There Unity's mother and Debo went to pick her up. By then months had passed, and they found a girl totally ruined, Debo told Lovell,

She had an odd vacant expression... the most pathetic sight. I was very shocked and I can't begin to imagine what it must have been like for my mother seeing her like that... But it wasn't just her appearance; she was a completely changed person, like somebody who has had a stroke.

When she got back to England there were calls for Unity to be brought up on charges of treason. But given her condition — she is often said to have been left with "the mind of a 12-year-old," and she had a sudden mania for Christian Science which displaced the fascism — she was simply left to her mother's care. Unity died in 1948, still dependent on her parents, after ten years of letters between the sisters flying back and forth expressing concern. ("Birdie is here & is so terribly pathetic, it really makes one miserable to see her," went one letter from Debo to Decca.) The cause was meningitis brought on by a sudden swelling around the bullet that was still in her head.

Most of the family dipped a toe in fascism at one time or another, particularly the Mitfords' father and older brother. But most of the sisters had some involvement, even met Hitler themselves, at one time or another. And Diana was interned, along with her husband, Oswald Moseley, for most of World War II. She'd continued to defend Hitler long after the war was over, a fact her descendant Charlotte Mosley claims is "mainly explained by her devotion and undeviating commitment to her husband." If that's correct, Diana manages to give an awfully convincing impression of a true believer in interviews, but no matter.

Only one sister who clearly dissented: Decca, the second-youngest. She fell in love with a man she read a book about. He was Esmond Romilly, a nephew of Churchill's, and when she finally met him in early 1937 he was just back from fighting with the International Brigades in the Spanish Civil War. In other words, he was a Red, through and through. By March of that year Decca had run away and married Romilly. The family was horrified by the scandal — "Muv cries all night & Farve has to make her tea, and they both look ten years older" — but Decca married Romilly in May. Yet Decca's marriage, and the anti-fascist beliefs she shared with her new husband, severed her connection to Diana for the rest of her life.

Oddly, though, Decca and Unity kept up with each other. A letter from Unity to Decca. pre-suicide attempt, sets out the compromise entailed:

Of course one can't separate one's politics & one's private life, as you know Nazism is my life & I very much despise that democratic- liberal- conservative- English idea of walking about arm- in- arm with one's opponent in private life and looking upon politics as a business or hobby; but I do think that family ties ought to make a difference. After all, violent differences of opinion didn't prevent you & me from remaining good friends did they. My attitude to Esmond is as follows – and I rather expect his to me to be the same. I naturally wouldn't hesitate to shoot him if it was necessary for my cause, and I should expect him to do the same to me. But in the meanwhile, as that isn't necessary, I don't see why we shouldn't be quite good friends, do you. I wonder if he agrees.

This sort of thing guaranteed that Decca would never be as close to her sisters again. And the start of the marriage was marked by poverty and a baby dead of measles. In the end, needing a new start, Romilly and Decca moved to America just before war broke out. He died patrolling the Atlantic for the Canadian Air Force a couple of years later, leaving Decca widowed with a ten-month-old in a foreign country and estranged from her wider family.

She recovered well, marrying a civil rights lawyer named Bob Treuhaft within two years and becoming a Bay Area civil rights activist and journalist. She would eventually make herself a household name The American Way of Death, which exposed the grifter-y practices of the funeral industry. Naturally the funeral industry hated her for it. She greeted their ire with classic Mitfordian good humor:

A new menace had loomed on their horizon: the Menace of Jessica Mitford. Headines began to appear in the undertakers' journals: JESSICA MITFORD PLANS ANTI-FUNERAL BOOK, AND MITFORD DAY DRAWS CLOSER!

When Mortuary Management began referring to me as Jessica tout court, I felt I had arrived at that special pinnacle of fame where the first name only is sufficient identification, as with Zsa Zsa, Jackie, or Adlai. Greedily I gobbled up the denunciations: "the notorious Jessica Mitford"; "shocker"; "stormy petrel."

Even in rebellion, in other words, Mitfords almost couldn't help themselves from getting in the thick of things. It was what they enjoyed.

It might surprise you to learn, after all of this, that the six Mitford sisters had barely a shred of formal schooling between them. There were occasional stints at boarding schools between them but none took university classes. Their parents didn't believe, in short, in educating girls.

So their wit was a product they cultivated themselves. If you read their letters — there are a couple collections but the best for this purpose is The Mitfords: Letters Between Six Sisters — you can observe the laboratory in action. There are so many nicknames — Susan, Bobo, Birdie, Boud, Hen, Henderson, Nard — that one begins to lose track. Special languages were not just a childhood trick either — one of my favourite phrases of theirs comes only when the sisters, in adulthood, begin themselves bearing children. The process of getting pregnant is often described in their books as follows:

Well, dear, I've smacked my ovary and taken it to Madame Bovary and the result is I'm in pig...

The Mitfords themselves produced entire books about their childhoods, the best known of which is Jessica's Hons and Rebels (sometimes Daughters and Rebels, its original American title).

Unity, Debo and I were thrown much on our own resources. As a lost tribe, separated from its fellow men, gradually develops distinctive characteristics of language, behaviour, outlook, so we developed idiosyncracies that would no doubt have made us a little eccentric to other children our age. Even for England, in those far-off days of the mid-1920s, ours wasn't exactly a conventional upbringing. Our accomplishments and amusements took distinctly unusual forms. Thus, at an age when other children would be occupied with dolls, group sports, piano lessons or ballet, Debo spent silent hours in the chicken house learning to do an exact imitation of the look of pained concentration that comes over a hen's face when it's laying an egg. Each morning she methodically checked over and listed in a notebook the stillbirths reported in the vital statistics columns of the Times.

I amused myself by giving my father daily Palsy Practice, which consisted of gently shaking his hand while he was drinking his tea: 'In a few years, when you're really old, you'll probably have palsy. I must give you a little practice now, before you actually get it, so that you won't be dropping things all the time.'

These eccentricities are funny but also obviously the product of a childhood spent feeling lonely and cloistered. The Mitfords were privileged in a way, born minor aristocrats. But the family was not rich, at least not rich in the way that titles like Lord and Lady might imply. No one could possibly nostalgic for an era when girls were kept boxed-up before marriage like this, even if it recalls the idylls of Little Women. Yet it gave the Mitfords the unique imaginative energy.

And even if that energy led them down some terrible, awful, very bad paths, there is still something about it that keeps us talking all these 80 years later.

There are, of course, still Mitford descendants kicking around. A few are even famous. The model Stella Tennant is Debo's granddaughter. And the artist Daphne Guinness is Diana's. But it seems to say something about the way things have changed that Guinness's nephew Stavros Niarchos is probably best known to you, anyway, for his association with what our present day delivers to us as famous, accomplished sisters: the Hiltons and the Olsen twins.

[Image by Tara Jacoby, from a photo of the Mitford family.]