"Let me see, I do not think that I have your address?"
With a grand air, Miss Monro drew a card from her hand-bag, and handed it to him. It was a somewhat dirty card, and the original address had been scratched out and another substituted in pencil.
Then, with a good many bows and gesticulations on Poirot's part, we bade farewell to the lady and got away.
"Do you really think this photograph so important?" I asked Poirot.
"Yes, mon ami. The camera does not lie. One can magnify a photograph, seize salient points that otherwise would remain unnoticed. And then there are a thousand details—such as the structure of the ears, which no one could ever describe to you in words. Oh, yes, it is a great chance, this which has come our way! That is why I propose to take precautions."
He went across to the telephone as he finished speaking, and gave a number which I knew to be that of a private detective agency which he sometimes employed. His instructions were clear and definite. Two men were to go to the address he gave, and, in general terms, were to watch over the safety of Miss Monro. They were to follow her wherever she went.
Poirot hung up the receiver and came back to me.
"Do you really think that necessary, Poirot?" I asked.
"It may be. There is no doubt that we are watched, you and I, and since that is so, they will soon know with whom we were lunching to-day. And it is possible that Number Four will scent danger."
About twenty minutes later the telephone bell rang. I answered it. A curt voice spoke into the phone.