This stone looked nearly the same, but it wasn't. It was the Wish Switcher Stone. The stone worked just like the normal one, except that it attuned itself to the next person who touched it.
For example (using Zoe and Athena), anything Zoe wished for herself, Athena got and anything Athena wished for Zoe, Athena got. Also, anything Zoe wished for Athena, Zoe got, and anything Athena wished for Zoe, Zoe got. (Confused yet?)
Zoe walked towards the spot where she usually met up with her friends before school. And as she approached Athena, she took out the stone, completely unaware that it wasn't the same stone she inherited from her grandfather.