We found Rivers lying on his back on the hill, with his hands clasped behind his head.
"I have been watching the windows," he said, "and making a mental map of the house. All the bedrooms seem to be situated at the back; the ordinary living rooms are in front. See--there is a light in only one of the rooms; there was a light in that room last night. It burns steadily, and without flickering; the room is occupied, but no shadow has appeared on the blind, nor has the light been shifted. Someone is sleeping there, and sleeping undisturbed. If we stopped here till daylight we should probably find that light still burning. Afraid to sleep in the dark, denoting a nervous organization. Ah, observe. Two rooms have just been entered; each person, entering, carried in a candle with him; the lights shift and waver; there are shadows on the blinds. One is the shadow of Mr. Nisbet, the other the shadow of Dr. Cooper; their bedrooms adjoin. Rather restless those shadows. We have the advantage of them; we can see them, they cannot see us lying here in black darkness. I am in my element, and can work out theories. I have done the same in country places in England, and the theories I have worked out there have led to very useful conclusions. Isn't there a German or French story of a man who sold his shadow to the devil? I can imagine occasions when our friend Mr. Nisbet would gladly sell his, for shadows are sometimes criminating witnesses. Those men do not seem in a hurry to get to bed. One has gone into the other's room; the flaring of the candle shows that he has left his door open. The shadows of the two men are now in one room. They walk up and down in their slippers--of that you may be sure. There is something so secret and mysterious going on in the house--which might be a prison or a private lunatic asylum--that the principal conspirators are careful to make no noise. They have no wish to disturb the sleeper in the third room, which, by a stretch of the fancy, we might suppose to be occupied by a dead person. By the way, did Dr. Cooper have time to bring his slippers with him from London? I should say not; therefore he is wearing a pair of Mr. Nisbet's or is walking in his stocking feet. Now they stop, now they walk about again, and now--yes, now they go into the room which the first man left. Science has been busily at work of late years, but it has not yet discovered a means of bringing sound to our ears as this glass which I am holding brings the figures of those men near to my eyes. There is the telephone, but you cannot carry a telephone about with you in a little pocket case. I dare say the discovery will be made one of these days. Mr. Nisbet is a couple of inches taller than Dr. Cooper, and as they are now standing quite still I know which is one, and which the other; therefore I shall presently know which is Mr. Nisbet's bedroom, and which Dr. Cooper's. If we could only hear what they are saying to each other! Speaking in whispers, of course--again for the reason that they do not wish to disturb the sleeper in the third room. Mme. Bernstein will inform us who it is who sleeps there. What do you say--a man or a woman?"
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."
"We shall be seen," whispered Bob, in great alarm.
"We are as safe," said Rivers calmly, "as if we wore caps that rendered us invisible, as in the fairy tale. As they stand side by side at the window, the position of the light enables me to see them clearly. They are Mr. Nisbet and Dr. Cooper. Provoking! What is it that Mr. Nisbet has just done? Why did you move, you fool of a doctor? But I guess what he did. He emptied the glass out of the window. Of course, of course; that was it. They have been making a chemical experiment, testing a liquid--to what end? Mr. Nisbet peers into the dark grounds, he stares straight at the hill upon which we are lying. Don't stir a finger. It is curious that criminals almost invariably overlook some slight circumstance which supplies the clew to their conviction. It has been so in thousands of cases. The window is closed, the blind is pulled down. See the shadows of the men as they approach and retreat, growing to monstrous proportions, dwindling to nearly natural size. The shadows of Fate. I suppose by this time the conference is at an end. It is. They separate. Each is in his own room. Ah, I see which room is occupied by Mr. Nisbet, and which by Dr. Cooper. The doctor gets into bed first. Out goes his light. Sleep the sleep of the just, doctor, if you can. Mr. Nisbet lingers; his is the greater stake. He is the principal, his companion is the tool. Take care, the pair of you; the dogs are on your track. Mr. Nisbet puts out his light; all the windows are masked except the window of the third room. Good-night, good-night."
These ingenious theories filled me with wonder, and I accepted them as if they were proved testimony; and I am positive, from the remarks made by Bob and Ronald, that they also accepted them as I did. Rivers chuckled, and said:
"It is a fine art, and we become masters only by long study. Now for Mme. Bernstein. She will not keep us waiting long."
She did not. In a few minutes the gate was opened, and the old woman appeared.