Pelagia & the white bulldog - B. Akunin

In the dying days of the Nineteenth Century, the small Russian town of Zavolzhsk is shaken out of its sleepy rural existence by the arrival from St Petersburg of a Synodical Inspector with a hidden agenda and a dangerously persuasive manner.
Meanwhile, in the nearby country estate of Drozdovka, one of the prized white Bulldogs - prized because of its one brown ear, and its propensity to drool - belonging to the cantankerous lady of the house has been poisoned. The old widow has taken to her bed, sick with fear that her two remaining dogs may face a similar fate, and the many potential beneficiaries of her will wait fretfully to see whether or not she will recover.
Sister Pelagia: bespectacled, freckled, woefully clumsy and astonishingly resourceful is summoned by the Bishop of Zavolzhsk to investigate the bulldog's death. But her investigation soon takes a far more sinister turn when two headless bodies are pulled out of the river on the edge of the estate.