"The evidence, then, you gave at the inquest," continued Rivers, "whether false or true (you see I am not disposed to be hard on you), was conclusive, and doubtless you were well paid for it. In the eyes of the law Mr. Nisbet's stepdaughter was dead, and he came into her fortune. The simplicity of the whole thing would be amusing if it were not tragic. But his task was not yet finished. He had committed an error of judgment in killing the wrong woman; the lady whom he had robbed of her fortune still lived, and it was imperative that he should get rid of her. He must have been in fear of detection, or he would have adopted some violent and summary measures to compass his objects. Being fearful of consequences he determined to kill her slowly, and it was also necessary that he should destroy her memory, that he should make her mind a blank, for if by any chance the news of the tragedy which had taken place in Lamb's Terrace reached her knowledge the game would be lost. According to the way I reason it out he hoped that the drugs he administered to her would cause her to die a presumably natural death, but the lady was obstinate, and refused to die as he wished. At length, weary of waiting, he calls you in to assist him." "You are on the wrong track," said Dr. Cooper. "I have never seen the lady." "You are in your right senses, I presume," said Rivers. "The lady happens to be in this house." "In this house?" "Do you wish us to believe you have not seen her?" "On my honor, I have not seen her." At this reference to his honor a queer smile crossed Rivers' lips. "There is a female here, as I was given to understand by Mr. Nisbet, one of his domestics, who was indisposed. But I have seen no one except Mr. Nisbet and an old woman who cooks for him, and with whom I have not exchanged a single word. Mr. Nisbet informed me that he wanted my assistance in certain chemical experiments he intended to make in Switzerland, and I consented to accompany him. It was a sudden proposition, and I had to make up my mind on the spur of the moment. When I first made his acquaintance he promised to assist me and set me up in a good way of business, but after the inquest I lost sight of him, and his promises were not fulfilled. Coming upon me suddenly a week ago in London, he said if I would assist him that he would fulfill his old promises. I would have come with him without this assurance. I was doing no business in London, and I was in debt; I have always been in debt everywhere; I am the most unfortunate wretch in existence. Now you have the truth of it." "What were you and Mr. Nisbet doing to-night before you went to bed?" "What do you mean?" "It is a plain question. You and he were together in this room. You poured some drops from a vial into a glass. Mr. Nisbet took the glass from you, dipped his finger into it, and tasted the stuff; then he threw the contents of the glass out of the window."