Humans try to better themselves. They find out that these betters are still just human, they are failures too. In the disappointment, there's a propaganda campaign to blame the failed bettered for all the problems of the world. But the failed bettered (and the not so failed betters) find out that the world had problems long before they existed, so they aren't to blame. Then they fight their oppressors for the right to exist.
There is a movie with many characters that have the same name as those in this book. The movie has a similar setting and takes place in the same general timeline. It's a good sci-fi action movie. To call the Allegiant movie an adaptation or interpretation of this book is like saying the McDonald's BigMac is an interpretation of the planet Jupiter.