In the book, Pratchett spends a lot of time deconstructing the idea of witches. Mostly he does so through Tiffany's musings. He also uses a witch we've seen before: Mrs. Proust, who runs a novelty shop in the big city. Tiffany and Mrs. Proust both clash with the superstitious view of witches. Tiffany usually wears green dresses, while Mrs. Proust is constantly shilling a new line of humorous poo-shaped products. But they both wear the pointy hat, and they both do what needs to be done. On the Discworld, being a witch means taking care of business.
The author creates the Cunning Man to underline the horror of witch persecutions. The Cunning Man is basically a spirit that can influence pliable minds. "Poison goes where poison's welcome," says Mrs. Proust, and the Cunning Man can only turn those whose minds are filled with hatred, rage, and envy. It resurrects itself every so often after being banished by a strong witch. (Guess which mega-witch banished it last time. Go on, guess. Hint: blue eyes.) Due to certain complications in her ironically nonexistent love life, Tiffany becomes the new target for the Cunning Man's relentless campaign to rid the world of witches. She finds herself hated by people she grew up with, because the Cunning Man feeds their minds with lies about the evil of witches.
Of course, no Tiffany Aching story would be complete without the Nac Mac Feegles, a race of tiny faerie folk sworn to protect her, if only they could stop boozing and brawling among themselves. They provide most of the comic relief in the novel, because Tiffany plays it pretty straight. As a bonus, they also welcome back into the fold Wee Mad Arthur, a policeman who grew up believing that he was a gnome.
I Shall Wear Midnight feels darker than previous Tiffany Aching outings, especially toward the middle, before she understands why the Cunning Man is after her. Once she does, however, she gets right down to kicking ass and taking names.
I think the best part of the story is Tiffany's strong characterization. She's very young, but she knows who she is, and she knows what needs to be done. She has the pride, power, and bossiness that comes naturally to all great witches. The second best part of the book is the supporting characters. No one can go it alone, and our Tiff gets plenty of help. There are the faerie folk, the young castle guard Preston, and other witches and possibly even a wizard. I shan't spoil the surprise, in case you're an avid Discworld reader who's plowed through all 30+ novels.
Tiffany Aching stories are marketed as YA, but I recommend this one for anyone who liked, say, The Hunger Games trilogy. It's got a strong female lead, plenty of colorful side players, a creepy villain, and great lessons about self-confidence, duty, and doing what's right.
Mr. Pratchett, the ending almost made me cry. How wonderful. Well done, sir, well done. I would bow and raise my pointy hat to you, if I had a pointy hat!