Looking from girl to girl (some of them new), Jon began to regret his decision to come back to the school with Karyn after going to the mall. Well, it was actually Karyn's idea to come back, to see if anything was different due to Jon's vague wish. But Jon went along with it. He told her that they could just go back to his house and use the stone to figure out what happened, but Karyn said that since the school was closer, it would be easier.
Well, she couldn't have been more right, unfortunately. The moment Jon and Karyn saw the mob of people running in panic from the football field, they knew that something "interesting" really was happening. So they went to check it out. It was the biggest mistake of their lives.
And now Karyn was one of the cheerleaders, part of Sarah's posse of friends, and she didn't want anything to do with Jon anymore.