The question was addressed to us, and we expressed our inability to answer it.
"I say a woman," continued Rivers, who was certainly in his element, as he had declared, "and until Mme. Bernstein favors us with her company we remain in ignorance as to who the woman is. Our little Barbara's sister? Perhaps. But Barbara describes her sister as being a lively young person, and no lively young person lies sleeping there. How do I arrive at that conclusion? Impossible to say. Mental cerebration, if you like. We work out plots as novelists do, or rather, they work out themselves. Concentration is the agent. The same process leads me to the conclusion that the conspirators yonder are walking and talking noiselessly because of their fear of being overheard. The same process leads me to the conclusion that they are quietly discussing an important and dangerous matter. How did Mr. Nisbet's stepdaughter meet her death? Asphyxiation caused by an escape of gas while sleeping in a bedroom almost hermetically sealed. But there is no gas in these parts, and their light is supplied by oil and candle. Therefore they are deprived of that means of causing death. What are they doing now? The shorter of the two, Dr. Cooper, holds something up to the light. The object is too small to be discerned at this distance, but I take it to be a vial. Not a wine bottle, nor a bottle containing brandy or whisky. A small vial. And now Mr. Nisbet hands his co-conspirator a wineglass; he holds that up also; the shadow is reflected on the blind, and you can see by the shape that it is not a tumbler. The vial in one hand, the wineglass--it may be a medicine glass--in the other, Dr. Cooper is pouring a few drops from the vial into the glass. He counts the drops; I can't see his lips move, but unless I am dreaming he is counting the drops. He puts down the vial, and Mr. Nisbet takes the glass from him. To drink? No. He dips his finger into the liquid, and puts that finger to his lips. He stands still a while; he is deliberating. Is it satisfactory, Mr. Nisbet? If it is, and you need a sleeping draught, drink it off, and wish your companion good-night. You do nothing of the kind. You come to the window; you draw aside the blind; you open the window."