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 memorized 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. Afterward, she enrolled herself in law school, where she finally put that memory to good use.