The Valley of Fear – Sir Arthur Conan Doyle – Platanus Publishing

He was too m 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.