This book is the final book in the trilogy His Dark Materials. I personally thought that the book was very good, but I was unsatisfied with the ending. The plot is very complicated and it is crucial that you read the first two books in the series, but mainly, Lyra, a young teenager has the exceptional gift of reading a truth telling device. In the second book, The Subtle Knife, she meets a boy of the same age named Will who also discovers a gift of his own, although he comes from a different world. Together travel through dangerous and important worlds until they discover that the fate of all the worlds depends on them and they must make decisions that are truly heartbreaking.
The first two books in the trilogy: The Golden Compass, The Subtle Knife. Another book by Philip Pullman is Lyra's Oxford which is not part of the series, and I have not read it.
I loved this book as well as the entire trilogy, but as I said, I was disappointed with the ending as I felt it was incomplete and it did not leave me at rest. I don't expect books to have happy endings, but I like it when they leave me feeling like the characters are more connected to each other than Lyra and Will were at the end of this book.