At 28 years old, Eleanor Catton is the youngest ever winner of the Man Booker Prize. And at 832 pages, her ambitious, intricate, spectacular novel, The Luminaries, is the longest book ever to win. It follows a densely-populated cast of characters as they orbit their way through the New Zealand gold-rush: each one on a path dictated by the movement of the stars.

It begins with a man named Walter Moody arriving in the bar of a grotty dockside hotel in January 1866. Twelve men are already present, all doing their utmost to conceal their mutual purpose. But as Moody falls into conversation with first one, then another, it becomes clear that a profoundly complex mystery is about to unfold.

Each section of the book is precisely half the length of the previous section: an immense feat of structuring and plotting which means that this novel starts as a gentle stroll and ends with the exhilarating sense of running downhill. When people disparage literary fiction, it is almost always by saying that these beautiful characters and sentences are all very well, but what about the plot? One could silence them all with Catton’s book (and wallop them with it if they continued to disagree).

As Catton explained in her victory speech, all her characters are engaged in transactions. Gold changes hands legally and illegally, openly and surreptitiously. Bullets seem to disappear in mid-air, while the influence of laudanum waxes and wanes. Only one relationship in this glittering affair defies the transactional philosophy and is instead (as love must always be) a gift freely given.

The novel, like the ever-shifting gold within it, is not what it first appears. What seems to be a historical thriller turns out to be something far more profound: an exploration of the power of lucre played out in front of a canvas of free will and determinism.

Catton was 25 when she began work on this, her second novel. Doubtless there will be those who feel she has been rewarded too young: that writers shouldn’t win when they’re young in case they can’t replicate their success. But the point of an extraordinary novel is that it leaves the writer behind. Some people write many brilliant novels, others write only one, which in no way diminishes the achievement. No-one can predict who will write lots of great books and who will peak early. Harper Lee didn’t write another novel after To Kill a Mockingbird, knowing she couldn’t compete with her own past. It’s why, as judges, we considered the books, not the authors.

You have to forget the writers, and give the prize to what you think is the best book of the year. I don’t know what I’ll do with my time now. But the books have just started arriving for my next judging project (the Independent Foreign Fiction Prize), so if you’ll excuse me, I’d better get back to the reading.