I now knew that John Wilson held the means for the crime - but what about the motive? He had come to Belgium on business, and had asked M. Déroulard, whom he knew slightly, to put him up. There was apparently no way in which Déroulard's death could benefit him. Moreover, I discovered by inquiries in England that he had suffered for some years from that painful form of heart disease known as angina. Therefore he had a genuine right to have those tablets in his possession. Nevertheless, I was convinced that someone had gone to the chocolate box, opening the full one first by mistake, and had abstracted the contents of the last chocolate, cramming in instead as many little trinitrin tablets as it would hold. The chocolates were large ones. Between twenty or thirty tablets, I felt sure, could have been inserted. But who had done this?

There were two guests in the house. John Wilson had the means. Saint Alard had the motive. Remember, he was a fanatic, and there is no fanatic like a religious fanatic. Could he, by any means, have got hold of John Wilson's trinitrine?

Another little idea came to me. Ah! You smile at my little ideas! Why had Wilson run out of trinitrine? Surely he would bring an adequate supply from England. I called once more at the house in the Avenue Louise. Wilson was out, but I saw the girl who did his room, Félicie. I demanded of her immediately whether it was not true that M. Wilson had lost a bottle from his washstand some little time ago. The girl responded eagerly. It was quite true. She, Félicie, had been blamed for it. The English gentleman had evidently thought that she had broken it, and did not like to say so. Whereas she had never even touched it. Without doubt it was Jeannette - always nosing round where she had no business to be -

I calmed the flow of words, and took my leave. I knew now all that I wanted to know. It remained for me to prove my case. That, I felt, would not be easy. I might be sure that Saint Alard had removed the bottle of trinitrine from John Wilson's washstand, but to convince others, I would have to produce evidence. And I had none to produce!

Never mind. I knew - that was the great thing. You remember our difficulty in the Styles case, Hastings? There again, I knew but it took me a long time to find the last link which made my chain of evidence against the murderer complete.

I asked for an interview with Mademoiselle Mesnard. She came at once. I demanded of her the address of M. de Saint Alard. A look of trouble came over her face.

'Why do you want it, monsieur?'

'Mademoiselle, it is necessary.'

She seemed doubtful - troubled.

'He can tell you nothing. He is a man whose thoughts are not in this world. He hardly notices what goes on around him.'