The Grave's a Fine and Private Place by 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.

Brought to shore, the dead man is found to be dressed in blue silk with ribbons at the knee, and wearing a single red ballet slipper.

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. But what could possibly connect the son of an executed killer, a far too canny police constable, a travelling circus, and the publican's mysteriously talented wife?