Captain's log - Stardate 2261.36

We've found the person that appears to be the crux of the timeline alteration - a woman named Edith Keeler, the founder and moving spirit behind the peace movement that Khan had embraced and taken to a whole new level by attempting to eradicate military units worldwide.

I knew Spock had found something - something I wouldn't like - by the way his posture stiffened. Looking at the screen I saw an obituary from the 1980s - Doctor Leonard McCoy and his wife, the former Edith Keeler, died in a plane crash. He married the woman?