Something is happening, and we don’t know down here what it may be. There could be a war breaking out. There was a war in heaven once, oh, thousands of years ago, immense ages back, but I don’t know what the outcome was. It wouldn’t be impossible if there was another. But the devastation would be enormous, and the consequences for us . . . I can’t imagine it.” So a terrified inhabitant of Cittagazze tells the witch Serafina Pekkala, but that is precisely what Philip Pullman has set out to imagine in this audacious sequel to his highly-acclaimed novel Northern Lights, winner of the Carnegie Medal.

When 12-year-old Will accidentally commits murder he finds himself fleeing for sanctuary through a window into another world. Arriving in a strangely silent yet balmy port, for a moment he feels safe but this is a refuge for which he will pay the highest price and in which he is destined to play an almost unimaginably profound role from the second he stumbles upon Lyra Silvertongue - the unforgettable heroine of Northern Lights.

This is fantasy for the millennium - fantasy at its most ambitious and most serious. In the tradition of Tolkien and C S Lewis, Pullman is working in the English line of what may almost be called “theological fantasy”, which is not to say that this cracking adventure does not move with the pace of an Indiana Jones movie.

This is rare storytelling by a master of labyrinthine creativity, and at the heart of it stands Pullman himself, challenging the very notion of Original Sin as Lord Asriel gathers monumental forces to make war on the Authority, Himself.

“Course, anyone setting out to do a grand thing like that would be the target of the church’s anger. Goes without saying. It’d be the most gigantic blasphemy, that’s what they’d say. They’d have him before the Consistorial Court and sentenced to death before you could blink,” says Lord Asriel’s manservant, Thorold. Quite.

Despite the thickness of the book, the pace of incident, nothing is being done purely for effect. In her essay “Some Thoughts on Narrative” from Dancing at the Edge of the World (Gollancz 1989), Ursula K Le Guin wrote, “We cannot ask reason to take us across the gulfs of the absurd. Only the imagination can get us out of the bind of the eternal present . . . leading us to the freedom that is properly human, the freedom open to those whose minds can accept unreality. ”

In Pullman we have such a mind and a story in which angels can communicate with both children and sub-atomic physicists. Young readers approaching the year 2000 may find the turmoil and occupations of Pullman’s parallel worlds less unfamiliar than some adults may assume. After all, they too live in a world at once medieval and ultra-modern. The appearance of a dead princess’s ghost can still make front-page news in a world where Chaos Theory is no longer regarded as science-fiction. Here, too, “the boundaries of the worlds are crumbling”.