I know what to do!
"I wish Karyn was here," Jon said.
"Why do you want Karyn here?" his mom asked.
Karyn didn't appear in the room. Jon thought that since his wish was about Karyn, it would grant it, since she was presumably holding her stone. But Jon's stone just didn't seem to work at all.
He looked down at it. It looked exactly like the other stone. But it wasn't. It was as if it were part of the other stone, but people couldn't use it to make wishes. This was not good.
And while all this was going through Jon's head, Karyn was about to make yet another wish.