On the ninth of January, now four days ago, I received by the evening delivery a registered envelope, addressed in the hand of my colleague and old school-companion, Henry Jekyll. I was a good deal surprised by this; for we were by no means in the habit of correspondence; I had seen the man, dined with him, indeed, the night before; and I could imagine nothing in our intercourse that should justify formality of registration.
The story unfolds in Robert Louis Stevenson's The Strange Case of Dr Jekyll and Mr Hyde