What is the resolution in The Third Wish by Joan Aiken?

The resolution of the story is that Dido Twite defeats the dwarf at the end by outsmarting him and using his own tricks against him. She tricks him into taking a "magical" potion that turns him into a harmless toad, and then she throws the toad into the well. This frees the boy, and Dido and the boy are able to escape from the castle.