raptornx01 said:
Esk's appearance didn't feel like an explanation at all. It felt more like a set-up/tease for some future story.
I couldn't disagree more with what I think you are saying, though I'll admit that I'm not sure what kind of explanation you thought there should be.
Esk, I think, is brought in for two reasons. First, people have been asking Terry for years "Whatever happened to Esk?" And wanting to know more about her. Thus, he amuses himself by putting her in what I take to be the last of the quartet of Tiffany books. But, Esk is not a witch--she's a wizard! And she can therefore do some things that witches can't do--like go back and find the origin of the cunning man, and engage in all kinds of time travel (including providing the "traveling now"). She serves as a necessary plot device to provide absolutely necessary information and warning to Tiffany in a way that no one else can.
Tiffany (and the readers) need to know the history (and power) of this evil spirit. He is one of Terry's best villains, both in himself (and his total disregard for those he uses) and even worse,in the way he corrupts the society existing when he reappears. His power is so great that he even gets Tiffany and the Boffo shop owner witch (whose name escapes me at the moment) to turn on each other. He destroys the ability to trust and encourages everyone to find someone else to blame for everything. Since he's dead, he can't be killed--only sent back until someone awakens him again. But if he takes over Tiffany with all her power, he would be much worse. That's why the other witches are prepared to kill Tiffany if she doesn't defeat him.