"My first step, therefore, was to seek assistance of the great botanist who is curator of Kew Gardens, and, after considerable difficulty and many experiments, we both arrived at the conclusion that it was the bean of a small and very rare plant peculiar to the oasis of the Ahir in the south of the Great Sahara. At Kew there was a stunted specimen, but it had never borne fruit, therefore we both searched for any other specimen that might exist in England. We heard of one in the wonderful gardens of La Mortola, near Mentone, and, after diligent inquiries, discovered that a firm of importers in Liverpool had sold a specimen with the beans in pod, which was delivered to a person named Turton, living in Bishop's-wood Road, Highgate, and planted in a small greenhouse there. I have not been idle," he added with a grin. Then, taking from a drawer in the table before him a photograph, he handed it to me, saying, "I have been able to obtain this photograph of Mrs Turton--the lady who purchased the plant in question." He held it out to me, and in an instant I recognised the face. It was that of the woman who had crept so silently through the rooms at Atworth--La Gioia! Briefly, I told him all that had transpired on that night, and declared that I recognised her features, whereat he grunted in satisfaction. "You have asked me to try and solve the mystery, and I have done so. You will find this woman living at a house called `Fairmead' in the road I have indicated. I have not only established the cause of the phenomena, but I have, at the same time, rediscovered the most extraordinary and deadly substance known in toxicology. As far as the present case is concerned, my work is finished--I have succeeded in making some of the vayana alkaloid. Here it is?" and, taking a small yellow glass tube, securely corked and sealed, he handed it to me. In the bottom I saw half a grain of tiny white crystals. I knew now why he was wearing gloves in his laboratory. "And have you seen this woman?" I asked the queer old fellow, whose careful investigations had been crowned with such success. "How did you know, on the following day, that it was La Gioia who had come in the guise of a dressmaker?" "I have seen her, and I have seen the plant. It is from one of the beans which I secured secretly that I have been able to produce that substance. I knew her by overhearing a conversation between Miss Wynd and her cousin on the following morning." "And the woman is in ignorance that you know the truth?" "Entirely. I have finished. It is for you now to act as you think fit." I expressed admiration for his marvellous patience and ingenuity in solving the mystery, and, when I left, it was with the understanding that, if I required his further assistance he would willingly render it. CHAPTER THIRTY. "LA GIOIA."