Back at his house, Jon was panicking.
He didn't know what that vague wish did, so he made a wish to find out, cluing him in on the fact that someone within range of the stone had been granted ten wishes. But who was it?
After another wish, he realized that it was Fred Orr, Sarah McMillan's cousin. But then the stone changed the information. His given name was still Fred, but his family named changed.
Apparently, he was already making wishes to change things. Jon figured that he still remembered Fred as Fred Orr because he heard the wish that gave Fred his wishes. So he'd most likely remember how things were before the vague wish and notice any changes made to reality. But that wasn't good enough. He needed to stop this before things got out of hand.
So with that, he made a wish to make it so that Fred could no longer make any more wishes ... but nothing happened. Could it be that that was considered as a contradiction? Feeling irritated, Jon realized that that was a very good possibility. The best thing Jon could do was track down Fred and make him say wishes that were mostly harmless, until his ten grantable wishes were done. Hopefully, Fred hadn't figured out yet that his wishes were coming true.
Meanwhile, back at his new home, Fred ...
