A sister is not a friend. Who can explain the urge to take a relationship as primal and complex as a sibling and reduce it to something as replaceable, as banal as a friend? Yet this status is used again and again to connote the highest intimacy. My mother is my best friend. My husband is my best friend. No. True sisterhood, the kind where you grew fingernails in the same womb, were pushed screaming through identical birth canals, is not the same as friendship. You don’t choose each other, and there’s no furtive period of getting to know the other. You’re part of each other, right from the start. Look at an umbilical cord – tough, sinuous, unlovely, yet essential – and compare it to a friendship bracelet of brightly woven thread. That is the difference between a sister and a friend.

The eldest of the Blue sisters, their leader, is Avery. She was born wise and world-weary. At four years old, she returned to their parents’ Upper West Side apartment after walking herself home from kindergarten and declared herself too tired to go on. But she did go on, she always has. Avery taught all the sisters how to swim the front crawl, how to make friends with the bodega cats by tickling them under the chin, how to shuffle cards without bending the corners. She hates authority but loves structure. She has a photographic memory; in high school she broke into their school’s records and memorised her entire grade’s Social Security numbers, then spent the remainder of the semester freaking kids out by referring to them by their nine digits.

She graduated from high school at sixteen and completed undergrad at Columbia University in three years. Then, she ran away to join an “anarchic, nonhierarchical, consensus-driven community,” otherwise known as a commune, before briefly living on the streets of San Francisco, where she smoked and, eventually, shot heroin. Unbeknownst to anyone in her family, she checked herself into detox a year later and has stayed clean ever since. Afterwards, she enrolled herself in law school, where she finally put that memory to good use.

They say you don’t know your principles until they become inconvenient to you, and Avery is proof of this. She is deeply principled and often inconvenienced. She might have liked to be a poet or a documentary filmmaker, but she is a lawyer. Now thirty-three, she lives in London with her wife, Chiti, a therapist seven years her senior. She has paid off all her college loans and owns furniture that cost almost as much as her tuition. She does not know it yet, but in a few weeks, she will implode her life and marriage in ways she didn’t think possible. Avery would like to be all backbone, but she is tender flesh too.

Two years after Avery was born, their parents had Bonnie. Bonnie is soft-spoken and strong-willed. Her language is the language of the body. By six, she could walk on her hands. By ten, she could juggle five tangerines at a time. She tried both ballet and gymnastics, but she never fit in among that flock of flexible, feminine girls. When she was fifteen, their father bought her a pair of boxing gloves after she punched a hole in her bedroom wall, and she found her true form.

Bonnie discovering boxing is probably how other people felt when they discovered sex. So, this is what all the fuss is about.

Bonnie worships at the altar of discipline. After silently watching her older sister’s adolescent decline, she vowed never to touch a drop of alcohol. Her drugs of choice are sweat and violence. This got her all the way to the IBA Women’s World Boxing Championships, the highest level of amateur competition in the sport alongside the Olympics, where she won silver in the lightweight division before turning pro. Unexpectedly, given her sport of choice, Bonnie is the gentlest of her sisters. She can get ice out of the tray without bashing it on the counter. Babies and dogs trust her instinctively. She is a terrible liar. Though her body is like a vaulted oak door, her nature is as transparent as a window. Now thirty-one years old and in what should be her fighting prime, Bonnie has quit both New York and boxing after a devastating defeat in her last fight. She fled to Venice Beach, Los An- Angeles, where she took a job as the bouncer of a dive bar.

Most people go through life never knowing what it’s like to have a calling, one that asks you to sacrifice the pleasure of the moment for the potential of a dream that may not be realised for years, if at all. It sets you apart from others, whether you want it to or not. It can be gruelling, lonely, and punishing, but, if it is really your calling, it is not a choice. This is how boxing felt to Bonnie. And yet, right now, you can find her in some backstreet of Venice, collecting empty pint glasses, helping tipsy women into the back of cars, and sweeping up cigarette butts, with no trace at all of the anarchic, ironhearted warrior she was trained to be.

Their parents wanted a son next but, after two miscarriages never spoken of again, they had Nicole, known always as Nicky. Of all the girls, Nicky was the most girl. She could blow a bubble as big as her head. She listened to teen pop into adulthood without irony. Her favourite hobby as a child was raising caterpillars to become butterflies by feeding them tiny pieces of squash. When she was ten, she bought her first underwire bra, just so she’d be ready. She’d had five boyfriends by the time she graduated from high school. She liked to pick out a week’s worth of outfits in advance, including underwear to match. She could apply a perfect cat eye with liquid liner in a moving taxi without smudging the flicks. Nicky was always popular with boys, but she had a knack for female friendship. She joined a sorority in college, a fact her sisters ruthlessly teased her for, but she didn’t care. Her sisters were often busy with their own careers, and she missed them, so she made a family of her friends.

If Avery was sensible and Bonnie was stoic, Nicky was sensitive. She was a carnival of feelings she never tried to hide. Sometimes she was the ecstatic swirl of a carousel, sometimes she was a bumper car collision, sometimes she was the still target waiting in the shooting gallery. She was born to be a mother, but her body had other ideas. After years of agonizing periods, she was diagnosed with endometriosis in her twenties. Though she died at twenty-seven, she was not a natural member of that club; she wasn’t the lead singer of a band, and she didn’t live particularly fast to die young. If you’d asked Nicky, she would have said she lived an extraordinarily ordinary life as a tenth-grade English teacher at a charter school on the Upper West Side, ten blocks from where she grew up. If it seemed a smaller existence than her sisters’, she never saw it that way. She loved her students and dreamed of one day having a family. Nothing about her life portended her death, except for the fact she was in pain.

A year after Nicky’s birth, their parents tried one last time for the long-awaited son. They got Lucky. Born at home by mistake in only fifteen minutes, Lucky wasted no time establishing her place in the family. No matter how old Lucky gets, she will always be the baby. In fact, once Nicky could speak, she quickly proclaimed Lucky my baby and insisted on lugging her tiny form with her everywhere. They remained inseparable, but Lucky did not stay small. She is five foot eleven. Their parents got four shots to create that so-sought-after thing: female beauty. With Lucky, they succeeded. Even her teeth, which are crooked with unusually sharp canines, give her smile a sensual, wolfish quality. Recently, without the approval of her agency, she chopped off most of her hair and bleached it white. Now, she looks like a combination of Barbie, Billy Idol, and a Siberian husky. Lucky became a model when she was fifteen and has worked all over the world, which is another way of saying she has been lonely all over the world.

When Lucky enters a room, it is like an electric eel slipping into a bowl of goldfish. She is sharp-witted and secretly shy. She taught herself to play the guitar while living in Tokyo and is pretty good but too self-conscious to ever perform in front of anyone. She still loves playing video games, loves any form of escape, in fact. Right now, she is living alone in Paris. She has said the words I need a drink one hundred and thirty-two times so far this year. That’s more than she’s said I love you in her entire life. In her apartment in Montmartre, she has the framed blue butterflies Nicky gave her before she died hanging above her bed, but she rarely sleeps. Lucky is twenty-six years old, and she is lost. In fact, all the remaining sisters are.

But what they don’t know is this: As long as you are alive, it is never too late to be found.

Excerpted with permission from Blue Sisters, Coco Mellors, Fourth Estate.