According to what I could see of the movie understanding that:
There were 9 aliens came to Earth after his planet was destroyed by an enemy species (so to speak), and in fact continues to Earth. The protagonist is the number "four" named John Smith, which is constantly changing identities, moving from one city to another. John has a guardian or conservator named Henri. The story takes place in Ohio, the last city to which John moved.
John enters as a high school student in Ohio, in high school befriends a boy named Sam, whose father was studying about aliens and one day disappeared, plus falls in love with Sara, which leads to the problem of his kind when they fall in love is forever.