Jon was planning on wishing Karyn over. He wanted her to be there so they could discuss what he had in mind for the stone. He was up for hours the previous night thinking about it.
But once he laid his hands on the stone, a feeling of excitement and power washed over him. It seemed to come out of nowhere.
He smiled to himself, thinking of all the things he could wish for. And then said "I wish Karyn was here and was naked and stupid and only cared about having sex with me." He was so energized by the feelings of power that he ran through the wish like a run-on sentence.
After the stone glowed and he put the stone down, though, the feelings of power were completely gone, replaced with feelings of horror at what he had done.
Karyn was standing in the middle of his room. She was completely naked and had a mindless grin on her face. And lust in her eyes.
Jon wanted to tell Karyn how sorry he was, but some reason, he couldn't. What was happening? Where did that feeling of power come from? And why did he make that wish?
