I am number four

At first, there were nine of them. They came from Lorien, which is one of the life existing planet. They came to Earth to hide from Mogadorians, who destroyed the planet Lorien and who are trying to kill them. These nine last children of Lorien can only be killed in the sequence of their numbers. John, who is the main character of this book, is number four. Numbers one, two and three are already killed by Mogadorians. John has three super powers. He moves to Paradise, and makes a girlfriend named Sarah. At first, no one knew that John was an alien, but finally, the Mogadorians find John and John tells Sarah the fact. John fought with Mogadorians with number six, his guardian, Sarah and some of his friends. He won the war, but he lost many people in the war.