"What I have related," I said in conclusion, "is under the seal of confidence, and is not to be mentioned unless the mystery is brought to light. Just at this moment I confess to feeling dispirited; the web of conjecture is so slight that I am oppressed by the feeling that we may, after all, be following a will-o'-the-wisp, and that there is no ground for the suspicions that have led me on." "That is one way of putting it," observed Mr. Rivers, "but as you suspect that a crime has been committed, would it not be a relief to you to find that there is no ground for the suspicion?" I was at a loss to reply to this question, and he proceeded. "It may be due to the occupation I follow, but I generally place the worst construction upon these matters. If I were otherwise inclined, I should place the worst construction upon this, and my belief is that Mr. Nisbet has been guilty of nothing less than murder. Every circumstance in the case points to the conclusion, which is strengthened by the impression he has produced upon me. He is a man capable of any desperate deed, or I am no judge of character. I am obliged to you for the confidence you have placed in me; it certainly renders me less powerless in the assistance I may be able to render. I have a starting point, you see. Just at present there are two questions in my mind to which we must endeavor to find an answer. First, what has become of the girl Molly? I should know how to work her if I could lay hands on her. Second, what is the meaning of the association of Mr. Nisbet and Dr. Cooper? To their former association, when Mr. Nisbet and his stepdaughter were living in Lamb's Terrace, where the poor lady met her death, there is an absolutely plain answer. Mr. Nisbet wanted a death certificate from a doctor who was imperfectly acquainted with the facts, and he paid Dr. Cooper to supply it. This certificate being accepted at the inquest, and the body cremated, Mr. Nisbet was safe. In the absence of proof, of what practical value would mere suspicion be? He could snap his fingers at it. But the circumstance of his taking Dr. Cooper suddenly and unexpectedly from London, and of the doctor being in his house at this moment, puzzles me." "Mr. Nisbet requires his assistance again," I suggested. "That is the natural inference, and we have to discover the exact nature of this required assistance. If bold measures are necessary we must adopt them." "I am ready. Have you any theory as to Molly?" "I can think of more than one. The girl was young at the time of the lady's death; Barbara is by no means bad looking; Molly was pretty, I dare say; she was poor, she was ignorant; Mr. Nisbet may have taken a fancy to her----" I interrupted him. "No, Mr. Rivers, I cannot entertain the theory that Molly consented to become Mr. Nisbet's mistress."