The Secret Passage by Fergus Hume — Read

Jennings had once witnessed a drama by Victorien Sardou, entitled -- in the English version -- Diplomacy. Therein a woman was unmasked by means of a scent. It seemed to him that perfume also played a part in this case. Why should Clancy, Mrs. Herne, Hale, Maraquito and Thomas use a special odor? "I wonder if they meet in the dark? " thought the detective, "and recognize each other by the scent. It seems very improbable, yet I can't see why they use it otherwise. That women should use perfumes, even the same perfume, is right enough. They love that sort of thing, but why should men do so, especially a man in the position of Thomas? I'll follow up this clue, if clue it is!"

The conversation with Juliet convinced Jennings that she knew of something connected with the matter, but was determined to hold her tongue. The fact that this knife was in her possession showed that she was aware of some fact likely to lead to the detection of the assassin. She might have found it when she came after the death to Rose Cottage, but in that case, had she nothing to conceal, she would have shown it to the police. Instead of this, she hid it in the attic. Jennings congratulated himself on his dexterity in securing this piece of evidence. There was no doubt in his mind that this was the very knife with which Miss Loach had been stabbed.