The Subtle Knife
is the second book in Philip Pullman's His Dark Materials
trilogy. In this book Lyra crosses into another world, and meets Will a boy from yet another world - our own. One thing to note is that this book needs to be read as part of the trilogy. The first book (The Golden Compass
) can just about be read on its own - although there are a few loose ends - but I would advise that to read the second book you need to have read the first and go on to read the third.
This book seemed to me to have a more sci-fi feel to it than the first, with Will and Lyra moving about between different worlds, and the possibility of interacting with the mysterious 'Dust' via scientific equipment. My feeling is that the books aren't really suited to the 12 year old readership which would be suggested by the age of Will and Lyra, but to a somewhat older readership. If you fit in to this category, but felt that the first book was too unsophisticated for you then you should still give the second a try, as you might find the sci-fi approach more to your taste.