I found this story on Futility Closet’s blog here.
“On Nov. 25, 1809, British diplomat Benjamin Bathurst was preparing to leave the small German town of Perleberg. He stood outside the inn, watching his portmanteau being loaded onto the carriage, stepped out of the light, and was never seen again.
“A nearby river was dragged, and outbuildings, woods, ditches, and marshes were searched, but no trace of Bathurst was ever found. A reward was offered for information, but none came forth.
“Bathurst had been urging Austria into war against the French, but Napoleon swore on his honor that he had played no part in the disappearance. The mystery has never been solved.”
Naturally, many conspiracy theorists speculate that his disappearance was supernatural. Most academics believe the more probable explanation: he was murdered. He already had to flee Vienna in light of approaching French forces, and had decided that the safest way to get back to London was to take a ship from Hamburg. He also traveled under a pseudonym. So there was clearly already the need for him to take significant safety measures.
According to Wikipedia, “The disappearance did not create much excitement at the time, since the country was infested with bandits, stragglers from the French army, and German revolutionaries. Additionally, murders and robberies were so common that the loss of one commercial traveller (which Bathurst was travelling as) was barely noticed, especially since at the time there were hardly any legal authorities in Prussia.”
News of his disappearance didn’t even reach England until several weeks later, when some thought that maybe he–sensing danger–disappeared and went into hiding. There was also some speculation that he could have been kidnapped for political leverage. If either of those two options were the case, no one ever heard from him or about him again.
Almost 50 years later, in 1852, a house nearby the inn where he disappeared was demolished. When the house came down, they discovered a human skeleton under the stable. The skull was fractured, as if by a heavy blow (not related to the demolition).
Bathurst’s sister, who was still living, traveled there to see the skeleton. But after such a long disappearance there wasn’t anything about it that could provide a conclusive identification.