The Valley of FearArthur Conan Doyle
The Valley of Fear
A coded warning sends Sherlock Holmes and Dr. Watson to Birlstone Manor. The answer lies in a secret that reaches back to a Pennsylvania mining town.
From the English edition
He was too much absorbed with his own thoughts to give any immediate answer to my remonstrance. He leaned upon his hand, with his untasted breakfast before him, and he stared at the slip of paper which he had just drawn from its envelope. Then he took the envelope itself, held it up to the light, and very carefully studied both the exterior and the flap.
Edition and source
Project Gutenberg eBook 3289 · English
Public domain in the USA; complete source text and Gutenberg license retained; no charge