The Sweetness at the Bottom of the Pie

Sweetness and the Bottom of the Pie by Alan Bradley

Yes, this is a book written for grown ups and yes, the main character is 11 years old. Flavia deLuce has a passion for poison, the vocabulary of an adult, and a bicycle named Gladys. Her mother died climbing mountains in the Himalayas and her father, Colonel de Luce, is just about as distant, showing more interest in his stamp collection than his daughters. It's part of the whole English reluctance to show affection and keeping a stiff upper lip, or something like that...
But things get shaken up a bit when a dead blackbird shows up on the porch at Buckshaw (the old mansion where the de Luces live) with a penny stamp stuck to it's beak. The next morning Flavia finds a dead man in the cucumber patch - well, he's not dead yet, but expires with a final word: "Vale." But who was he, and more important, who killed him? Was it the Colonel who had secretly argued with the stranger the night before, or Dogger, the dependable but unstable gardener (who still suffers from his experiences in Japanese POW camps)? Maybe he died from eating a slice of Mrs. Mullet's horrible cream pie? Whoever it was, Flavia is determined to find out with the help of her chemistry knowledge and Gladys.