The stone glowed, granting Zoe's wish, but it wasn't granted to Zoe, Athena, or Zelda. Instead, it was granted to someone else within the 50-foot radius and that person was Karyn, who was coming to the Gibson house to see if the stone was there. Jon no longer existed, but that didn't mean that the stone couldn't still exist. Maybe someone else in the family inherited it, like Zoe or Michelle. If so, then Karyn could still get Jon back ... if she was able to get her hands on it and make a wish.
Karyn was walking up to the front door, trying to think of what to say to whoever greeted her. She had a feeling that the Gibson family might not know who she was, since Jon never existed.
And that's when it happened. Knowledge suddenly appeared in her mind, telling her that someone nearby had the wrong wishing stone, and instead had something called The Random Stone. She knew exactly how this other stone worked and knew that whoever was making wishes might not know that their wishes would be granted to someone else within a 50-foot radius, like her.
She had to get into the Gibson house and stop whoever was making wishes! She began pounding on the door, trying to get someone to open up.