The film storyline may turn out to be a fusion between 'Ender's Game' and its parallel novel 'Ender's Shadow', focusing on the important elements of both. Technically speaking, both books take place at exactly the same time, and they both focus on the same events at the Battle School, but from the points of view of two different characters.
Some elements we'll be seeing in the movie, like the 2nd Alien Invasion, were only briefly mentioned in 'Ender's Game', yet 'Ender's Shadow' covers them in greater detail. Orson Scott Card says that 'Enders Game' is an unfilmable book, not because of too much violence, but because everything takes place in Ender's head. 'Ender's Shadow' sounds like a logical choice to improve and enhance viewers' perspective on the events at the Battle School. Per the audiobook of 'Ender's Shadow' the afterword by Orson Scott Card mentions very clearly that this film is technically an amalgam of both books to create a tellable story since the story does take place largely in Ender's head. Obviously there is significant license taken but this does not damage the overall story.
