Imagine my delight when the first three pages of Ann Leckie’s Ancillary Justice boggled me with pronouns. They’re all female: she and her; no he, no him. This Elizabeth Moon-like space opera with big ships and engineering settings inhabits a new conceptual landscape, but is it simply a local effect? Ursula Le Guin’s The Left Hand of Darkness (1969) uses ambi-sexual characters to question sexual determination, but the male-female dyad is still the basis for that society. Nicola Griffith’s Ammonite (1992) features an all-female planet, but the people really are all female: the planetary virus kills the males. Ancillary Justice changes human social coding in a subtly different way: “She was probably male, to judge from the angular maze-like patterns quilting her shirt”. This grammatical contradiction does Escher-like things to our assumptions about the characters, and how their society codes gender. It makes us look again.

In this novel, which won not just one but three big sf awards - the 2014 Hugo, Nebula and the Arthur C Clarke - Ann Leckie has written a believable, genderless narrative voice, confidently and consistently in a novel nearly 400 pages long. She has constructed a society in which gender is irrelevant, even down to a language that lacks gendered words. This is beyond refreshing: it is game-changing, a major technical achievement. I often rage about the older sf novelists’ failure of vision. They spent their creative energies thinking through the technical implications of an invention, yet still assumed that society would continue into the 2300s as if it were the 1950s. By showing that gender isn’t necessary, Leckie has made a fundamental change in how to write about people in a future society.

Another social code that Leckie tinkers with is the insistence of this society – the Radchaai - on wearing gloves. This might sound like an opportunity for Pythonesque facetiousness, but not wearing gloves in Radchaai culture is on a par with our own taboo about exposing genitalia: unthinkable, deeply shaming, only for an infant, profoundly disruptive unless under sanctioned circumstances, a correctable, primitive state. She makes us think again about what taboos about bare skin and gender are for, and how they are enforced.

In Ancillary Justice the Radchaai are an immense militarised and space-faring empire, controlled by the Lord of the Radch (the noun denoting ultimate power is masculine, even if the Lord is she). Leckie says in the interview at the back of the UK paperback edition that the Roman Empire contributed some elements to the Radch. I think the Radchaai’s formal patterned behaviour might also come from imperial Japanese history or from the Manchu dynasty, and its feudal system of houses and clientage suggests the Holy Roman Empire as well.

These are the elegant, mannered aspects to their culture. Underneath, they are ferociously efficient, because each Radchaai ship has multiple bodies, or ancillaries, to lead, enforce and administrate its military operations. These are reanimated humans – called corpse soldiers by their conquered populations - connected directly to the ship’s artificial intelligence (a line of thought that originated in Anne McCaffrey’s The Ship Who Sang in the 1960s), and organised into cohorts of twenty. Each ancillary can access all the data from all the others, making them an unbeatable intelligence force and military unit. They are commanded by lieutenants, young officers of good family from the Radchaai echelons, whose rampant snobbery is becoming a problem.

The plot of Ancillary Justice follows Breq, formerly One Esk Nineteen, an ancillary of the One Esk cohort from the ship Justice of Toren, who has been on a private mission for twenty years. We follow her quest in its later stages, while catching up on the events that brought it about. Thus we learn how the apparently unassailable military and political forces of the Radchaai are being corrupted from the inside. Breq’s back story and current struggles to stay on mission take us to different worlds: an ice planet called Nilt, and a humid swampy planet called Shis’urna. Her last call is at a heavily populated unnamed spaceport where the Radchaai consul and her officials represent the urbane Radch velvet glove over the armoured fist. Breq’s mission is revenge, for an unimaginable act of treachery and casual murder that will do your head in.

The One Esk ancillaries are on planet when young Lieutenant Awn is forced to order a massacre of local citizens. When Awn arrives back on ship for an enforced transfer, One Esk (but not the AI), realises that the AI’s ship memory has been tampered with, because there is something going on in the lower levels of the ship that she cannot see and doesn’t understand. One Esk Nineteen is ordered to kill, and escapes in a pod before her ship explodes, the only survivor. Twenty years later, Breq is on Nilt, looking for the one thing that can defeat the Radchaai’s corruption and divert the empire from self-destruction. She finds a drug-addled body in the snow that she recognises, another lieutenant from her earlier career (these ancillaries live forever in successive bodies). One Esk had not liked Lieutenant Seivarden as she had liked Lieutenant Awn, yet she drags Seivarden into resuscitation and starts to puzzle out why she is on Nilt. Where Breq is. Is it coincidental that Seivarden, who had been lost in an act of murder and treachery a thousand years earlier, has reappeared just as Breq’s secret mission of revenge is reaching its most dangerous phase?

Leckie constructs the story in a familiar back-and-forth chapter pattern of backstory, current events and cliff-hangers (in one case, a bridge-hanger). But, unlike too many graduates of dreary MFA creative writing courses, Leckie is a natural, skilled storyteller, not a wannabe author. This novel is a classic page-turner, for the plot’s excitement, drama, tragedy and diabolical intrigue. It is also profoundly intelligent, because the beautifully imagined sociological framework for the Radch drives the action, and shows us how and why a person must act in this or that way. There is a little bagginess and second-guessing during the action in the second half of the novel, with portentous things being said by one character, and nodded at by another, leaving the reader none the wiser. Not that it matters: everything is explained and we hang on for the pleasure of the ride.

In epic sagas of galaxy pitted against galaxy, the range that people have to travel in space is of course unimaginable, as are the numbers of the Radch planets and solar systems. Yet the epic sagas are effectively a combat between two people, with some extras offering help or hindrance. This is something we’ve learned to live with, and some seriously brilliant inventions have been imagined to shrink the distances, skip over the light years, and keep humans alive as they voyage among the stars. Leckie does an excellent job of correcting the conceptual imbalance between the vastness of space and the incapacity of the human body to live long enough to see any of it, because her immortal ancillary minds live for as long as space is wide. Thus the story of this ancillary’s search for justice across an empire can unfold at a believable speed. In Ancillary Justice Leckie has found a way to relate the human and familiar to the scale of her epic plot.