I turned over the events of the day, and the more I considered them the less comprehensible they appeared. No one had followed the omnibus either on foot or in a vehicle, as far as I could see; and I had kept a careful lookout, not only at starting but for some considerable time after. Yet, all the time, Mrs. Schallibaum must have been following. But how? If she had known that I was intending to travel by the omnibus she might have gone to meet it and entered before I did. But she could not have known: and moreover she did not meet the omnibus, for we watched its approach from some considerable distance. I considered whether she might not have been concealed in the house and overheard me mention my destination to Thorndyke. But this failed to explain the mystery, since I had mentioned no address beyond “Kensington.” I had, indeed, mentioned the name of Mrs. Hornby, but the supposition that my friends might be known by name to Mrs. Schallibaum, or even that she might have looked the name up in the directory, presented a probability too remote to be worth entertaining.