The documents in the case - Dorothy L. Sayers

The bed was broken and tilted grotesquely sideways. Harrison was sprawled over in a huddle of soiled blankets. His mouth was twisted . . .
Harrison had been an expert on deadly mushrooms. How was it then that he had eaten a large quantity of death-dealing muscarine? Was it an accident? Suicide? Or murder?
The documents in the case seemed to be a simple collection of love notes and letters home. But they concealed a clue to the brilliant murderer who baffled the best minds in London.

'She combined literary prose with powerful suspense, and it takes a rare talent to achieve that. A truly great storyteller.' Minette Walters