Long-term readers of this series on the Hugo awards may recall that it started by raising the question of why critics sneer at science fiction. Now that I've read up to the ninth award-winner, Philip K Dick's The Man in the High Castle, I'd be tempted to put the question a different way – largely unprintable, but definitely containing the words "so-called" and "fools".

Before anyone accuses me of setting up straw men in the form of these doubting critics, I should admit that I was once among their number. I know the ignorance of which I speak. I also know the cure: to read the Hugo award winners from 1960-1963. Robert Heinlein's Starship Troopers, Walter M Miller Jr's A Canticle for Leibowitz, and Heinlein's Stranger in a Strange Land are classics by any reckoning, and they all influenced culture and literature far beyond the confines of the SF community. The Man in a High Castle is better still. It has helped shape an entire field of modern fiction: alternate history. It's the definition of genre-defining.

Its effectiveness can be judged on just how familiar the premise will seem even to those who haven't read the book: Roosevelt was assassinated during his first term, the Axis powers won the second world war, the US was divided by the victors, and the world – of course – is very different as a result.

Many other counterfactual books were written before this one. The point is not that it was the first, but that it was – and remains – such a fine example. Almost everything about it works, even the writing. One of the many stories told about Philip K Dick is that he was a mine of great ideas, but a bottomless pit for amphetamines, and that his habit affected his ability to write elegantly. Certainly, that's true for some of his books, but here the prose is mainly spare and effective. Occasionally, maybe, he was typing faster than he could think. Taken out of context, sentences such as the following can seem odd and off-putting:

"Brief instant, as if I rose to the surface and saw unencumbered. Life is short, he thought. Art, or something not life, is long, stretching out endless, like concrete worm."

But taken together, they add up to a whole that is coherent and vivid. There's plenty of tasty political intrigue and tension in a story strand about a spy's attempts to inform the Japanese about Nazi plans to use nuclear weapons against them. But it's the focus on a few other more ordinary, small-scale characters that really brings home the magnitude of the horror in this alternate reality.

For example: Robert Childan sells antique American collectibles to the Japanese and loses all dignity in simultaneously hating and longing to be like his imperial masters. Frank Fink creates these "antiques" in a factory and spends his life hunted, hiding his Jewish identity under a fake name but earning his living in a way that seems certain to bring him unwanted attention. Juliana, Frink's ex-wife, strikes up a relationship with an Italian truck driver, only to discover he has murder in mind …

These are real humans rather than conventional heroes. They are bewildered, afraid and overwhelmed by their circumstances. Atrocities touch them mainly as distant rumours. The murder of just about everyone in Africa, for instance, is reported only in passing, and the fact that we hear as little about it as the characters makes it all the more chilling.

I'd almost be tempted to compare this to something by Raymond Carver (the two writers share an air of quiet desperation, and a power that comes through things left unsaid) if there weren't also so many of Dick's trademark head-spinning riffs on the nature of reality. Nothing in the book is as it seems. Most characters are not what they say they are, most objects are fake – and the history that is supposed to imbue the artefacts Childan's customers long for is shown to be entirely intangible. What differentiates a cigarette lighter Roosevelt was holding when he was assassinated from an exact copy? Nothing we can perceive, anyway.

History and fiction become even more confused in a book-within-the-book (called, perplexingly, The Grasshopper Lies Heavy) which presents another counterfactual scenario in which the Allies won the war, but the British Empire came out with all the power. These ideas are then completely nuked when the I-Ching – which most characters play, and which Dick said guided his hand as he wrote – suggests the world in the second book might be the real one …

It's a mark of Dick's achievement that he can keep us transfixed as he guides us through this labyrinth. Though he provides no easy answers, leaves all his plot strands deliberately trailing and gives us nothing more to grab hold of than a delicious ambiguity, we are left feeling entirely satisfied. It's some book.

Next time: Way Station by Clifford D Simak.