Basically, there is a planet called Lorien and the (really awful) bad guys attacked it. To save their race, the Loriens send nine kids to earth along with their protectors. The nine are destined to return to Lorien and restart everything. But now the bad guys are on earth and hunting the kids. They must be killed in order, one to nine, which is a sort of protective charm. When we enter the story, One though Three have been killed and we follow the story of number Four as he discovers his really cool magical abilities and learns more about his past.
In the sequel, we continue to follow the intense stories of the Loriens that are still alive. Both books are really well written. They are captivating and exciting. I highly recommend them. For the most part they were clean. There is violence, but it wasn't overly graphic. Lore is a bit conceited (he names the planet and race after himself!) but it doesn't ruin the writing or the story. I you've seen the movie, READ THE BOOK! It's a million times better!