Black Maria

A novel by Diana Wynne Jones, published as Aunt Maria in the United States. A family is forced to stay with their Aunt Maria, a seemingly helpless old woman who, along with a coven of witches, hold a sleepy town in their iron grip.

Tropes used in Black Maria include:

Adults Are Useless: Mig and Chris's mother seems not to notice that she is being bewitched. However, when Mig finally makes her see it, she rapidly becomes very useful indeed.
Anticlimax
And I Must Scream: Antony Green, who was locked under a hill for years.
- Possibly also the fate of Aunt Maria. She is turned into a tiny, toy version of herself and set out at sea, with it being left ambiguous as to how aware she is of her fate.
Baleful Polymorph: Chris gets turned into a wolf. He doesn't enjoy it. Additionally, Aunt Maria's ex-caretaker was turned into a cat, but she chooses to stay that way. Also, Maria's daughter is turned into a wolf too (Does NOT end well).
- Mig and her mother and the neighbor's husband are all briefly turned into cats to help them with time traveling. Mig, at least, finds it very enjoyable.
Brainwashed: Mig's mother gets this treatment. Also the entire town seems to have at least a little bit of this.
Buried Alive: Antony Green, oh my god.
Disappeared Dad: The protagonist's father.
Exact Words: When sent by Maria to kill Chris while he's in wolf shape, the bespelled townspeople intentionally kill Maria's daughter, who had been turned into a wolf by Maria some years before.
Mama Bear: Mig and Chris's mother once she's cured of the whole 'brainwashed' thing.
More Than Mind Control: Part of Maria's magic is that she just talks people into doing whatever she wants. Just talks and talks until her ideas are implanted into someone's head, making the victim think she's right.
Not Quite Dead: Mig's father drove off a bridge, but the murder turns out to have been staged.
Our Ghosts Are Different: Antony Green. He gets better.
People Puppets: Mig gets this treatment when she wakes up in the local orphanage, which is basically a brainwashing camp.
- Not the first one in the town either, they never worked
Selective Deafness: Aunt Maria pretends not to hear anything that would be impolite, leading to a particularly funny scene:

Chris: And a hat on the mat where I shat!
Aunt Maria: What's that?

Stable Time Loop: When the heroes travel to the past to learn something key to the plot, they set in motion the events that led to their "present".