The Subtle Knife is where Philip Pullman's Dark Materials trilogy moves from a slightly foreboding children's fantasy to a truly dark, frightening story. The story moves rapidly between worlds; initially we encounter Will in our own Earth, then we move to the world Lyra has escaped too, but this is haunted by phantoms that prey on adults and children on the cusp of puberty.
Despite its familiarity, Will's world is a dark one too. His mother has some form of delusional illness, and as it becomes clear that the family is being targeted because his absent father had found some secret information, Will's life suddenly becomes terribly uncertain. Putting his mother in a place of safety Will accidentally finds his way to Lyra's world and receives a powerful tool that allows him to travel between worlds.
Back in Will's Oxford, scientist Mary Malone is on the verge of discovering that her Earth is actually linked to all the others, and that the object of her studies - dark matter, Dust, is a clue to how everything hangs together. This in turn makes her the target of unknown forces and she too escapes into an alternative space.
The rest of the novel which further illuminates the relationship of these key individuals too each other and the wider battle that is taking place, a battle in a war that transcends the different universes.
As in most trilogies, book two is a bridge between the beginning of a novel and the climax. But Pullman expertly uses this to flesh out the universe. While setting it in a dark fantasy universe, the novel is particularly effective because it plays on the fears of every child - the lose of ones parents, fear of the unknown and, in particular, the unfathomable conspiracies of adults. There's a particularly clever approach by creating monsters that only attack adults, and children growing into adulthood. A memorable scene has these otherwise invisible creatures clustering around a unknowing boy who is on the verge of becoming a man. In a few weeks they'll destroy him, but in the meantime he runs and plays with the others.
It is no wonder that Pullman's Dark Materials have become classics. They turn the ordinary into the extraordinary, and leave every reader yearning for more. The Subtle Knife lays the basis for the most powerful of the trilogy and its impossible not to immediately reach for The Amber Spyglass as soon as this is finished.
Pullman - The Northern Lights