All works of magic acknowledge Mystra as their Lord, so no defense Tabitha had used could have kept the ring on her finger when Mystra summoned it. As the ring flew off her finger into Mystra's palm, she protested. "Silence, foolish mortal." replied Mystra and Tabitha found herself shutting up.
Mystra's refined magic sense, and Adrian's memories, told her that the world she found herself on was a low-magic world. That would have to be changed. But how had this extraordinarily powerful artifact found itself on a world where the most powerful magician could barely turn cream into butter? Mystra interrogated the item itself. As it told its story, Mystra gave the terrible laugh of a goddess. Of course!
Shapechanging was no difficulty at all, as Mystra assumed the shape of an old woman. Working against the flow of time was a greater challenge--curiously, this strange world seemed to lack of a god of time--but Mystra's powers, in which her confidence was growing by the second, proved sufficient. She thrust the ring into the purse she had created, and left it in a convenience store. As was inevitable, an eager young man came running up to her with it.
Mystra rummaged through the purse and came up with the ring. "Here you are. Put this on your finger!"
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As the young man turned away, unknowingly facing his difficult destiny, the old woman vanished.