His Dark Materials Trilogy. Side Note: Don't think about the religious implications as you read this book. If you do think about them, you will find yourself either upset or questioning a lot of your personal beliefs (unless, of course, you already believe what is being written).
A children's classic that—back in the 1960's—gave the world a science fiction heroine: a bright, awkward, spirited girl named Meg Murry who travels through time and space to find her missing scientist father and save the universe. –MK - Esquire.com