Sarah turned towards Jon. "Is this true?" But he wasn't there. While the two girls were in their heated argument, Jon used the opportunity to slip quietly away back to his bedroom. And once there, he grabbed the stone, intending on making a wish. His "experiment" might have to be ended early, but he clearly made a time limit as part of the wish, so maybe there was no way to do it.
As he stood there, trying to think of a wish, he heard someone banging on his locked bedroom door.
"Open up, you little dweeb!" Karyn yelled. "I know what you're up to!"
