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.