The documents in the case

The grotesquely grinning corpse in the Devonshire shack was a man who died horribly -- with a dish of mushrooms at his side. His body contained enough death-dealing muscarine to kill 30 people. Why would an expert on fungi feast on a large quantity of this particularly poisonous species. A clue to the brilliant murderer, who had baffled the best minds in London, was hidden in a series of letters and documents that no one seemed to care about, except the dead man's son.