The Weed that Strings the Hangman's Bag (2010)

This is the second book in the series by Alan Bradley about the highly intelligent 11-year old Flavia deLuce. She continues to follow her passion for chemistry and poisons and befriends a puppeteer and his assistant after their van breaks down in her town of Bishop's Lacey. While their van is being repaired, they camp out on the grounds of a neighboring farm and promise to put on two shows for the residents of the town. At the end of the second show, the puppeteer is electrocuted. Flavia uses her unique knowledge to help the local constabulary find the guilty party. She is able to flit about the village and learn stuff because few take her seriously.

"You are unreliable, Flavia," he said. "Utterly unreliable."
Of course I was! It was one of the things I loved most about myself.
Eleven-year-olds are supposed to unreliable. We're past the age of being poppets: the age where people bend over and poke us in the tum with their fingers and make idiotic noises that sound like "boof-boof" -- just the thought of which is enough to make me bring up my Bovril. And yet we're still not at the age where anyone ever mistakes us for a grown-up. The fact is, we're invisible - except when we choose not to be.

They are starting to take notice of her, however.

"Dammit!" Inspector Hewitt shouted, leaping to his feet. "Sorry, Vicar. But why haven't we found these things out, Sergeant?"
He glared from one of his men to the other, including both in his exasperation.
"With respect, sir," Sergeant Woolmer ventured, "it could be because we're not Miss de Luce."

Now the long wait for the third book in the series.

My rating for this book: ++++