I believe I have found my Flavia de Luce for tweens. Sheila Turnage’s Three Times Lucky isn’t quite a mystery in the Nancy Drew sense -- it's better. Her heroine Mo LoBeau attempts to discover who murdered an ornery old neighbor, while also searching for lost pets and lost parents. She’s smart, industrious, and sassy. I loved that Turnage lets Mo experience real emotions (like getting sick with shock when she finds her guardian missing). And that her sidekick Dale doesn’t let Mo play the orphaned kid card all the time. As Dale, the child of a alcoholic father, tells her, they're all throwaways.
It looks as though Turnage might revisit the town of Tupelo Landing, North Carolina, in the future – her website hints at it. But I hope murder doesn’t follow Mo around. She deserves to be more than Miss Marple.