How to Stop a War Before it Begins

"Oh, don't mind me...I'm only trying to stop a war before it's even started and save half the people in this room from dying. Fate loves making me her bitch which means I have a lot of information. Albus can explain. I need sleep." What if Harry went a bit further back than he expected instead of moving on when he talked to Dumbledore at Kings Cross. harry/albus!friends