This book is so amazing I can't even explain my excitement to write this review!
Summary from wikipedia because I can't exactly explain it:
In a futuristic society the world is controlled by a new government and "The Population Police" who have decreed that no family shall have more than two children. These laws having been brought on supposedly by overpopulation, severe famine and death. Any child being born third or after in a family is a "shadow child" not to be seen by anyone or they will be taken away and killed along with their family and anyone who harbors them.
Luke Garner is a third child. His two older brothers Matthew and Mark go to school and have futures, but Luke must stay hidden, he can never have a job or get married or leave the farm. Luke was allowed to play outside on his family's farm and the woods, until the developers came. New homes are built next to Luke's farm and the woods are torn down, now he is no longer allowed outside, no longer allowed to eat dinner with his family in case he might be seen. Luke is miserable, until one day he sees a girl's face in a window, a window of a home that already has two children. Luke has found another third child and one day he dares to meet her.
The other third child is Jen and her father works for the Population Police as a spy trying to overthrow the corrupt government. Jen introduces Luke to things he's never experienced, television, computers and junk food, things only the rich and government officials are allowed to have. Jen is planning a rally of third children who will march in front of the country's leader demanding their right to exist in freedom. Luke and Jen get into a fight because Luke does not want to go to the rally, but they make up before Jen leaves.
Luke feels terrible for not going with Jen to the rally. He waits anxiously at home for word of what has happened, but a week passes and there is nothing so Luke sneaks back to Jen's home to look for her, unaware that the security system brings Jen's father rushing home, that's when Luke learns than Jen has been shot dead on the steps of the president's home along with every other third child who attended the rally. Jen's father Mr. Talbot warns Luke that he is in danger because he logged on to the third child chat room Jen had set up and that the Population Police are on the way there right now and quickly hides Luke when the other officers show up at his home. Mr. Talbot tells Luke that he will supply Luke with a fake ID card so that the government believes he is someone else, someone with the right to live. The story ends with Luke dressed in new clothes riding in a car with his new identity as Lee Grant the son of barons heading off to his new life. This leads us into the second novel in the series "Among the Impostors" where Luke is sent to a school far away with his new fake identity.