This was a case when Jon's "precautionary" wish came in handy. Even though he wasn't in hearing range of Sarah's unfortunate wish, his memories didn't get altered and he still remembered how things were supposed to be.
He and Zoe caught up with her and he grabbed the stone away from her. "I'll take my stone back, thank you."
"Yeah," Zoe said, "At least I was going to keep it in the family, Kiki."
Jon frowned. "Kiki?"
"Yes?" Kiki asked. "I know you...you were always nice to me..."
"What sort of game are you playing, Sarah?"
"Bro, you popped a gasket or something? That's Kiki McMillan...the school's head cheerleader...I don't even know anyone named Sarah...except maybe that dumb cat."
Kiki frowned. "I think...I need some answers..."
"You and me both," Jon said.
