What is the end of among the imposters about?

Answer 1

Among the Imposters is book 2 of 7 in the Shadow Childrenseries by Margaret Peterson Hendrix.

There is a pretty great summary of the book available on wikipedia, here is the "end":

Luke finally realizes who Jason really is and attacks him with a history book, causing the phone to get disconnected, and knocks Jason out. He comes up with a cover story for the Population Police officer at the other end and gets Jason down to the nurse's office. He calls Mr. Talbot, a double agent working with Population Police, and convinces him to come to Hendricks. When another officer comes, Mr. Talbot convinces them that Jason is lying about the third children and has Jason arrested along with Nina, his "accomplice" at the nearby Harlow's School for Girls, even though she has done nothing. Luke is later given the choice to leave the school, but he decides to stay at Hendricks and help the other third children.

Answer 2

In the book "Among the Impostors" by Margaret Peterson Haddix, the story ends with Luke leading a group of kids to safety after a failed uprising at the Population Police school. They are able to escape and find a new place to hide, setting the stage for the next book in the series.