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.
But, if I reached no satisfactory conclusion, my cogitations had one useful effect; they occupied my mind to the exclusion of that unfortunate draught of tea. Not that I had been seriously uneasy after the first shock. The quantity that I had swallowed was not large—the tea being hotter than I cared for—and I remembered that, when I had thrown out the lump of sugar, I had turned the cup upside down on the table; so there could have been nothing solid left in it. And the lump of sugar was in itself reassuring, for it certainly would not have been used in conjunction with any less conspicuous but more incriminating form of poison. That lump of sugar was now in my pocket,
