Saving Them One last time (book one)

After a world ending war Harry learns that much of what he knows is a lie. He gets a chance to save the world or not its up to him. How will he act to the people from the first time know that he knows. Will he find new friends, save the people he couldn't before, or even save the whole world again.

Because Theodore Nott has no confirmed actor I am putting Thomas Brodie-Sangster as Theodore