The Weed That Strings the Hangman's Bag (Flavia de Luce #2) by AlanBradley

Flavia de Luce, a dangerously smart eleven-year-old with a passion for chemistry and a genius for solving murders, thinks that her days of crime-solving in the bucolic English hamlet of Bishop’s Lacey are over—until beloved puppeteer Rupert Porson has his own strings sizzled in an unfortunate rendezvous with electricity. But who’d do such a thing, and why?