AS WE MADE OUR way across town the following morning to pay our mysterious “visit,” Poirot’s mood was as changeable as the London weather, which could not make up its mind between sunny and cloudy. At one moment he would appear to be pleased with himself and at ease, and the next he would furrow his brow as if worrying away at something.

We finally arrived at a modest house on a narrow street. “Number 3 Yarmouth Cottages,” said Poirot, standing outside it. “From where do you know this address, Catchpool? It is familiar to you, no?”

“Yes. Hold on a moment. It will come to me. That’s right—it’s Samuel Kidd’s address, isn’t it?”

“Indeed. Our helpful witness who saw Nancy Ducane run from the Bloxham Hotel and drop two keys, even though Nancy Ducane could not have been at the Bloxham Hotel just after eight o’clock on the night of the murders.”

“Because she was at Louisa Wallace’s house,” I agreed. “So we’re here to give Mr. Kidd a scare, are we, and find out who put him up to lying?”

“Non. Mr. Kidd is not at home today. He has gone to work, I expect.”

“Then . . .”

“Let us play a little game, called Knock-and-See-Who-Comes-to-the-Door,” said Poirot with an enigmatic smile. “Go ahead. I would knock myself if it were not for my gloves. I do not wish to make them dirty.”

I knocked and waited, wondering why Poirot expected anyone to come to the door of a house whose only known occupant was elsewhere. I opened my mouth to ask him, then closed it again. There was, of course, no point. Wistfully, I remembered a time (less than a fortnight ago) when I believed that asking a straight question of someone who knew the answer was a worthwhile thing to do.

The front door of number 3 Yarmouth Cottages opened, and I found myself looking into the large eyes of a person who was not Samuel Kidd. At first I was puzzled, for this was a face I did not know. Then I watched as terror twisted the features, and I knew who it had to be.

“Good morning, Mademoiselle Jennie,” said Poirot. “Catchpool, this is Jennie Hobbs. And this, mademoiselle, is my friend Mr. Edward Catchpool. You might remember that we talked about him at Pleasant’s Coffee House. Allow me to express my profound relief at finding you alive.”

That was when I knew for sure that I knew nothing. The few paltry scraps of certainty upon which I had been relying had proved themselves untrustworthy. How the deuce had Poirot known he would find Jennie Hobbs here? It was simply impossible! And yet, here we were.