There was a pause. Lamb’s surface irritation was all gone. His mind, slower than Miss Silver’s, but eminently competent and impartial, bent itself to weighing the arguments she had used. He did not allow himself to be hurried. He knew his own pace and kept to it. In the end he said,

“That’s right-it wasn’t Oakley-he couldn’t have done it.” He spoke as to an equal, quite without rancour, and continued in the same tone. “Any idea who did do it?”

She said gravely, “Someone who knew that Mr. Oakley was coming over.”

He whistled.

“How do you make that out?”

“I think it follows. I feel sure that the murderer knew of the telephone conversation between Mr. Oakley and Mr. Carroll- I think it quite apparent.”

Lamb’s eyes bulged.

“You’re not going to tell me you think it’s Pearson! I can’t swallow that.”

Miss Silver smiled.

“I shall not ask you to do so. We know that Pearson was listening to the first of the two conversations, the one which was terminated by Mr. Carroll. He did not, however, hear the second, when Mr. Oakley rang up to say that he was coming over. I considered it practically certain that there would be a second extension, to Mr. Porlock’s bedroom, and I have ascertained that this is the case. Now consider for a moment. Mr. Carroll had been playing upon the nerves and upon the fears of the whole company. How tightly strained must the murderer’s nerves have been-how intensely he must have been wondering whether Mr. Carroll really had any hold over him, and how he meant to use it. The party begins to separate for the night. He sees Mr. Carroll enter the study and shut the door. He may even hear him calling the exchange. Do you not think that he would wonder whether Mr. Carroll was about to impart his information to the police? If he could slip into Mr. Porlock’s room he could listen in on the extension and find out. I suggest that this instrument should be examined for fingerprints without delay. If they correspond-and I think they will correspond -with the prints taken early this evening from the mantelpiece in the hall and from the panelled side of the staircase, there will be a good deal of support for my theory.”

“Whose prints do you expect to find?”

Miss Silver shook her head.

“Pray allow me to continue. The murderer hears Mr. Oakley say that he is coming over. I think it possible, in fact probable, that he only reached the extension in time to hear this second conversation. He would have had to get upstairs and watch for an opportunity of penetrating into Mr. Porlock’s room.”

Lamb gave another of his grunts, usually a sign of interest.

“Well, what did he do next? I suppose you can give us an eyewitness account!”

Miss Silver continued to knit.

“I fear not. I can only tell you what I believe may have happened. He would, of course, immediately realize that Mr. Oakley might be used as a scapegoat. The circumstances of Mr. Porlock’s murder make it quite clear that the murderer is quickwitted and resourceful. He would, I think, see his chance of disposing of Mr. Carroll with very little risk to himself. He would calculate how long it would take Mr. Oakley to get here, and he would have to allow for his coming by car. The distance between the two houses being a good deal less than a mile, the difference between driving and walking would not be very great. Since the garage at the Mill House is at some little distance, I should suppose that he would wait for not more than five minutes before descending to the billiard-room, probably by the back stair.”

“The billiard-room?”

“I think so. Part of it lies under Mr. Carroll’s room, and it therefore has windows giving upon the court where the body was found. These windows, like the ones above, are all casements, and they are not very far from the ground. Having climbed out, he would have to go as far as the edge of the gravel sweep and provide himself with a handful of pebbles. He throws these up at Mr. Carroll’s window. As the window below was probably open at the time, it is possible that traces of gravel may be found on the billiard-room floor.”

Lamb jerked round on his subordinate.

“Go and have a look! Get Hughes, and tell him to try the telephone extension in Porlock’s room for prints-door-handles inside and out-window-fastenings in the billiard-room. Tell him to look slippy. He’d better start with the telephone. Let me see-where’s Jones? Put him in the billiard-room till it’s been gone over. And tell Jackson no one’s to leave the drawing-room till I come.”

Sergeant Abbott departed with regret. He would have preferred to stay and hear whether Miss Silver had anything more to say. This being the case, he did his errands in remarkably good time and returned with an air of vicarious triumph to report two or three pieces of small gravel just inside the billiard-room window.

Lamb grunted.

“Well, Miss Silver, it seems you’ve hit the nail on the head. Perhaps you will tell us now whose prints you think we’re going to find?”

Her needles clicked, the pink ball revolved. The triumph had been all Sergeant Abbott’s. She spoke gravely.

“I have been a very short time in this house. I have not, therefore, had my usual opportunities of making contacts or coming to conclusions. But, even on a very short acquaintance, there are things which cannot be overlooked. At any time before nine o’clock-”

Lamb picked her up sharply.

“Nine o’clock?”

She inclined her head.

“Coffee was brought into the drawing-room just before nine o’clock. The gentlemen joined us very shortly afterwards. Up till then, if I had been asked which of the guests in the house was the one most likely to have murdered Mr. Porlock, I should have been very much inclined to indicate Mr. Carroll. He made a very disagreeable impression on me. I thought him crooked and unscrupulous, and when it came to a question of motive he seemed to have a stronger one than anyone else. Proof that he had been concerned in treasonable correspondence with the enemy would certainly have meant a serious term of imprisonment, if not the death penalty. Even if the charge were not fully substantiated, he would be ruined professionally.”

Lamb was leaning forward, heavily intent.

“And what happened after nine o’clock? He wasn’t murdered for another hour and a half.”

“My suspicions became directed elsewhere. When Mr. Carroll began what he was pleased to call his entertainment I naturally kept a very close watch upon everyone. Let me remind you of my position. I was in the sofa corner next to the fire and therefore very well placed for observation. On my right, sharing the sofa, was Mrs. Tote. In prolongation of the end of it, and rather out of the circle, was Miss Masterman. Mr. Carroll stood in the space between her and the armchair occupied by Mr. Tote. Miss Lane, Mr. Justin Leigh, and Dorinda Brown were on the sofa opposite mine. Miss Brown had the coffee-table in front of her. Mr. Masterman was standing up before the fire-”

“Yes, yes-we’ve had all that!”

Miss Silver continued to knit.

“As you will see, I was most advantageously placed. It is true that I should have had to crane my head rather uncomfortably in order to watch Mr. Masterman’s face, but as it was not necessary for me to do so, this did not signify. Almost at once my attention became fixed upon Miss Masterman.”

Frank Abbott moved so sharply as to suggest protest. The Chief Inspector stiffened, his whole mass seeming to become more solid.

Miss Silver went on placidly.

“I had been a very short time in the house, when I realized that it contained two very unhappy women. Both Mrs. Tote and Miss Masterman were carrying a heavy load of anxiety and grief. In Mrs. Tote’s case, I discovered that she was unhappy about her husband’s sudden rise to wealth and her separation from her much loved only child. She spoke quite frankly on these subjects, but I discerned a deep uneasiness as to the methods by which so large a fortune had been made. I thought that she was not quite sure whether there had been a step farther-into crime. I did not myself consider Mr. Tote very seriously. I think he probably went upstairs after his interview with Mr. Porlock and talked violently to his wife about what he would like to do to him. She made a half-admission to this effect. I did not think that the man who had planned to murder Mr. Porlock would have been so foolish as to threaten him, or to advertize his bad temper as Mr. Tote did on that Saturday evening. I therefore set the Totes on one side. Miss Masterman was unhappy in quite a different way. When I first saw her she seemed to be living within herself-there seemed to be no contact with the outer world. She looked strained and ill, and I received the impression that she was waiting for something. After I had seen and talked with Sergeant Abbott I thought her frame of mind consistent with the supposition that she and her brother had inherited money to which she felt they had no claim. She seemed quite sunk into herself, quite abstracted, as if even a murder could not disturb what had become a habit of thought. When we came into the drawing-room after dinner she drew away from the circle about the fire and took up a newspaper, which screened her face. I do not think she was reading. I watched her, and she never turned a page. But when Mr. Carroll began his so-called entertainment she was, I think, startled out of her apathy. He had a very vivid and dramatic manner-everyone was watching him. I watched Miss Masterman. She did not lay the newspaper down, but she lowered it a little. She did not look at Mr. Carroll. Her right hand tightened on the paper so hard that it tore. She did not notice that I was looking at her. Her attention was wholly fixed upon something else. I followed the direction of her eyes and saw that she was looking at her brother. He had set his coffee-cup down upon the mantelpiece-I was in time to see him do so. As I have already remarked, I could not see his face without making an effort, but it was quite easy to see his hand setting down the coffee-cup-quite easy and, I thought, quite sufficient. Mr. Carroll had been addressing a series of highly provocative remarks to Mr. Tote. I did not take them very seriously. He was, in my opinion, merely baiting the person most likely to respond. After I had intervened with some light remark Mr. Carroll turned his attention to Mr. Masterman. He said much less to him than he had done to Mr. Tote, and there was much less apparent reaction, yet it was at this moment that Miss Masterman’s attention and my own became engaged. Currents flowing beneath the surface are sometimes very strongly felt. Miss Masterman felt something which roused her. I was myself aware of a sudden extreme tension. It might have been difficult to trace this tension to its source if it had not been for one thing, a slight but curious physical reaction. The hand with which Mr. Masterman put down his coffee-cup was perfectly steady. It was his left hand. The cup was put down without the slightest jar. The right hand, which was hanging by his side, was steady too. But both thumbs twitched uncontrollably. It was one of those involuntary movements of which a person may be hardly aware. I am quite sure that Mr. Masterman was not aware of the twitching until he looked down and saw it. He showed great presence of mind, sliding one hand down into his pocket, and putting the other behind him as if spreading it to the fire. It was all very smoothly and naturally done, but instead of allaying my suspicions it heightened them. I found myself believing that Miss Masterman had seen what I had seen, and that she placed the same construction on it. In these circumstances, I thought it probable that she would seek an interview with her brother. I do not know if you remember that her room is opposite mine. The gallery which runs round three sides of the hall gives access to two distinct bedroom wings. Miss Brown, Miss Masterman, and I have rooms in the right wing on this side of the house. The room used by Mr. Porlock is in the left wing, on the same side as the drawing-room and billiard-room, as are also the rooms occupied by the Totes, Mr. Carroll, and Mr. Masterman. I did not undress. I waited with my door a little ajar to see whether Miss Masterman would leave her room and go round the gallery to the other wing. She did so almost immediately. By going to the end of the passage I could see that she went as far as Mr. Masterman’s door. She knocked on it and waited.”