I soothed the girl down, pointed out to her that Mr. Ryland had probably been suffering from the enemy of his race⁠—dyspepsia. In the end I sent her away quite comforted. But I was not so easily satisfied myself. When the girl had gone, and I was alone, I took out my notebook, and ran over the letter which I had jotted down. What did it mean⁠—this apparently innocent-sounding missive? Did it concern some business deal which Ryland was undertaking, and was he anxious that no details about it should leak out until it was carried through? That was a possible explanation. But I remembered the small figure 4 with which the envelopes were marked, and I felt that, at last, I was on the track of the thing we were seeking.

I puzzled over the letter all that evening, and most of the next day⁠—and then suddenly the solution came to me. It was so simple, too. The figure 4 was the clue. Read every fourth word in the letter, and an entirely different message appeared. “Essential should see you quarry seventeen eleven four.”