When Max, Fang, and the rest of the Flock fly through a waterfall they end up in a world unknown to them. A world where everyone has either wings or parts of a serpent. A world where they fit in. Hawksong/Maximum Ride cross.

WARNING: Major spoilers if you have not read the fifth book. As such, I can't quite give a decent summary without some sort of spoiler, either... Basically this story takes place after the events of the fifth book, focused primarily on Prentice.