In the first half of the nineteenth century, an epidemic swept Europe: arsenic poisoning. Available at any corner shop for a few pence, arsenic was so frequently used by potential beneficiaries of wills that it was nicknamed "the inheritor's powder." But it was difficult to prove that a victim had been poisoned, let alone to identify the contaminated food or drink since arsenic was tasteless.

Then came a riveting case. On the morning of Saturday, November 2, 1833, the Bodle household sat down to their morning breakfast. That evening, the local doctor John Butler received an urgent summons:...