FIRST, a warning. The hotly-anticipated first volume of Philip Pullman’s Book of Dust trilogy is over 500 pages, and it’s an exhausting if exhilarating glimpse into the author’s continued — verging on tortured — metaphysical curiosity.

In this substantial work, Lyra — the outspoken heroine of Pullman’s His Dark Materials trilogy — is a helpless baby who endearingly babbles nonsense with her daemon. We meet her through a new kid on the block, Malcolm Polstead, from whose point of view the story is told. He is an impossibly wise and popular 11-year-old only child whose parents run the busy Trout Inn near Oxford, close to a crumbling priory where gentle old nuns live. They have in their care the six-month-old Lyra for safekeeping.

How she came to be at the priory, and how Malcolm plucks her from danger during a flood of biblical proportions to deliver her to safety in his canoe La Belle Sauvage, is the gist of this brilliantly constructed story.

It’s set ten years before Northern Lights, the first of the Lyra novels, and will continue roughly ten years after His Dark Materials, when Lyra is 20 years old.

Described by the author as neither a prequel nor a sequel to His Dark Materials, but an “equel” that sits beside it, he has said this new trilogy has been driven by his desire to get to the bottom of Dust, the troubling dark matter of the original books; so it follows that if — if — Lyra is the physical manifestation of Dust, the literal winding back of time to her babyhood might take us closer to discovering its origins. A tantalising idea.

When Malcolm — who, on top of homework and helping his parents in the pub (where he overhears some useful adult conversations) also assists the nuns in the priory kitchen — first meets Lyra they experience an instant bond, as illustrated by the friendly behaviour of Asta and Pantalaimon, the pair’s daemons (guardian angels?). Almost immediately, however, we’re aware of dark adult forces at work: Lyra is at risk of kidnap by different groups of people.

In true Pullman form, it turns out they’re representatives of the ideological struggle between a “despotic and totalitarian organisation which wants to stifle speculation and enquiry” and “those who believe thought and speech should be free”.

It doesn’t take long for the author’s infamous antipathy towards organised religion to emerge. Malcolm and Lyra live in a political climate of “obsequious submissiveness to the religious authorities”, where some favoured organisations find their power and influence enhanced while those who support the secular line of freedom of thought and speech work surreptitiously, and “at continuous risk of discovery”.

The parallel forces, which take the form of clearly sketched human characters, are quickly outlined: the ominous CCD, or Consistorial Court of Discipline, an agency of the Church which “disappears” heretics and unbelievers, of which Lyra’s estranged mother is a member; versus the rather more likeable Oakley Street underground organisation, which Lyra’s much admired father belongs to, and which employs the genial scholar Hannah Relf to interpret the responses to questions asked of its prized truth-telling device - alethiometer - regarding Lyra’s whereabouts.

Into the mix is thrown a silver-tongued murderer whose daemon is a rasping three-legged hyena. He has knowledge of the Rusakov gravitational field, which is linked to the Dust phenomenon and whose discovery means “consciousness can no longer be regarded exclusively as a function of the human brain”. He alone wants to kill Lyra.

THUS the scene is set: the rivals enter a deadly race to get to Lyra first. Each attempts to exploit Malcolm’s guilelessness to discover what their enemies are up to.

Unlike Harry Potter, Pullman’s “ordinary” protagonist possesses no wizardly powers; rather, he is visited by the aura of a very human ocular migraine, which nevertheless makes him feel special, as if he is the chosen, Enlightened, one. It is his level-headed practicality that steers Lyra and his perplexing companion Alice to the new world through the most terrifying and fantastic experiences. This is no Enid Blyton adventure story.

The most unsettling part of this tale, whose ambiguous time-zones suggest both the Middle Ages and modernity, is the League of St Alexander, the youth arm of the CCD which infiltrates Malcolm’s primary school. Named after a boy who converted to Christianity then reported his parents and had them killed for not believing in Jesus Christ, the League encourages children to report “wicked enemies” who are “working against the true faith”. Many become sneaky wee clypes. Teachers disappear. A culture of fear ensues, at the same time as an underground resistance movement. A younger nun at the priory turns out to be a CCD spy, while Malcolm is recruited by Oakley Street, the side Pullman apparently prefers.

His own resistance to black-or-white doctrinal reductionism here translates less as an attack on old-school Christianity than as a Blake-like parable about the perils of modern-day religious extremism (though Pullman’s publisher has warned readers not to draw too many parallels with what’s going on in the modern world).

All the same, the unquestioning and deferential Sisters Benedicta and Fenella (“these are mysteries we mustn’t enquire into”) do appear to get swept away in the flood, like the old guard that neglected to keep up with the times and now finds itself forced to make way for a new order. A warning to Christianity to look to its laurels, or wake-up call to all humanity?

The temptation to over-analyse every twist and turn is ever-present here, and I can’t help but suspect that Pullman enjoys throwing down the intellectual gauntlet to those who are up for it. Younger readers may find it difficult and to them I’d say just sit back and enjoy the ride. It’s certainly thought-provoking, though perhaps more benign than expected.

Which, of course, may just be the calm before the real storm.

La Belle Sauvage: The Book of Dust Volume One, by Philip Pullman, is published by David Fickling Books in association with Penguin Random House priced £20. The book will be available in hardback, ebook and audiobook (narrated by Michael Sheen).