dorothy and the wizard of oz

Here is the text from when they meet each other:

Presently they heard a solemn Voice, that seemed to come from somewhere near the top of the great dome, and it said:

"I am Oz, the Great and Terrible. Why do you seek me?"

They looked again in every part of the room, and then, seeing no one, Dorothy asked, "Where are you?"

"I am everywhere," answered the Voice, "but to the eyes of common mortals I am invisible. I will now seat myself upon my throne, that you may converse with me." Indeed, the Voice seemed just then to come straight from the throne itself; so they walked toward it and stood in a row while Dorothy said:

"We have come to claim our promise, O Oz."

"What promise?" asked Oz.

"You promised to send me back to Kansas when the Wicked Witch was destroyed," said the girl.