The Grave's a Fine and Private Place- Alan Bradley

Flavia is enjoying the summer, spending her days punting along the river with her reluctant family. Languishing in boredom, she drags a slack hand in the water, and catches her fingers in the open mouth of a drowned corpse. Flavia needs to put her super-sleuthing skills to the test to investigate the murder of three gossips in the local church, and to keep her sisters out of danger.