The Return Address That Does Not Exist
Holmes kept his counsel for the remainder of that day, and for the greater part of the next. I had learned, at much cost to my patience in earlier years, that to press him at such a time was not only useless but positively injurious to his processes of thought, which are as intolerant of company as a photographer's dark-room is of light. I therefore occupied myself with my practice, looked in upon two patients in Marylebone, and returned to Baker Street in the late afternoon of the second day to find my friend in his old chair, in his old dressing-gown, staring into the fire, with the *Post Office Directory* open upon his knees.
"Watson," he said, as I came in, "I have been a fool. Only the common sort of fool, I hope — not the distinguished sort. Sit down. I want you to go to Chelsea for me tomorrow morning."
"On what errand?"
"On the errand of confirming that a number in a street does not exist. It is a task in which I have an almost Oriental faith: no one, Watson, ever looks for a house that is not there. We assume that what we are sent to find will be findable. It is a weakness that I intend to turn to our advantage."
He handed me a slip of paper. On it, in his small exact hand, he had written: *11 Cheyne Row, Chelsea.* And below it, the instruction, which I could not at first understand: *Do not knock. Observe, and walk past.*
"This is not the writer's address?" I