They were both very young when it happened.
The only reason they played with each other was because she lived next door. The boy, a fairly serious-minded child, was actually quite bright for his age. She, on the other hand, was not. There always seemed to be an unnecessary silliness about her. It was a regular trait of hers to mock him about some of his ideas. When he discovered the stone, he had no intention of telling her about it, nor anyone else for that matter. But, as time went on, the temptation to share his knowledge regarding the magical properties of it, got the better of him. He felt sure that she would scoff at the idea that it could actually do what he said it could; that couldn’t be helped. It wouldn’t matter, anyway. He would swear her to secrecy.
So, the day came when he told her in strict confidence that he possessed a magic stone that enabled him to disappear. Of course, she didn’t believe a word of it. After a lot of wrangling about how stupid she thought it was and how truly amazing he thought it was, he showed it to her, but he wouldn’t let her touch it. As far as she could see there was nothing at all remarkable about it, it was just a stone. When he insisted that it had magic powers that would amaze her, she demanded a demonstration. At first he was reluctant to let her see what it could do, but finally, after reminding her that she was still under oath, he agreed.
For the sake of secrecy, she agreed to meet him in the park across the road; not a thing that either of them would normally be allowed to do. There was a small wooded area where they could go, allowing him to show her how it worked, away from prying eyes. When he was happy that they could not be seen, he took the stone out of his pocket. He placed it in the middle of his palm and closed his fingers over it. He clenched his fist tight and brought it up to his chest. With eyes closed, he began to murmur the incantation.
She smiled at his performance.
When the last few syllables had been spoken, he opened his eyes.
She was gone.