Bill went out and Antony knelt, watching eagerly.

"I thought so!" he cried. "I knew it couldn't have been that."

"What happened?" said Bill, coming back.

"Just what you would expect. The sunlight came, and the shadow moved back again all in one movement."

"And what happened yesterday?"

"The sunlight stayed there; and then the shadow came very slowly back, and there was no noise of the door being shut."

Bill looked at him with startled eyes.

"By Jove! You mean that Cayley closed the door afterwards as an afterthought-and very quietly-so that you couldn't hear?"

Antony nodded.

"Yes. That explains why I was surprised afterwards when I went into the room to find the door open behind me. You know how those doors with springs on them close?"

"The sort which old gentlemen have to keep out draughts?"

"Yes. Just at first they hardly move at all, and then very, very slowly they swing to-well, that was the way the shadow moved, and subconsciously I must have a.s.sociated it with the movement of that sort of door. By Jove!" He got up, and dusted his knees. "Now, Bill, just to make sure, go in and close the door like that. As an afterthought, you know; and very quietly, so that I don't hear the click of it."

Bill did as he was told, and then put his head out eagerly to hear what had happened.

"That was it," said Antony, with absolute conviction. "That was just what I saw yesterday." He came out of the office, and joined Bill in the little room.

"And now," he said, "let's try and find out what it was that Mr. Cayley was doing in here, and why he had to be so very careful that his friend Mr. Gillingham didn't overhear him."

CHAPTER XIII. The Open Window

Anthony's first thought was that Cayley had hidden something; something, perhaps, which he had found by the body, and but that was absurd. In the time at his disposal, he could have done no more than put it away in a drawer, where it would be much more open to discovery by Antony than if he had kept it in his pocket. In any case he would have removed it by this time, and hidden it in some more secret place. Besides, why in this case bother about shutting the door?

Bill pulled open a drawer in the chest, and looked inside.

"Is it any good going through these, do you think?" he asked.

Antony looked over his shoulder.

"Why did he keep clothes here at all?" he asked. "Did he ever change down here?"

"My dear Tony, he had more clothes than anybody in the world. He just kept them here in case they might be useful, I expect. When you and I go from London to the country we carry our clothes about with us. Mark never did. In his flat in London he had everything all over again which he has here. It was a hobby with him, collecting clothes. If he'd had half a dozen houses, they would all have been full of a complete gentleman's town and country outfit."

"I see."

"Of course, it might be useful sometimes, when he was busy in the next room, not to have to go upstairs for a handkerchief or a more comfortable coat."

"I see. Yes." He was walking round the room as he answered, and he lifted the top of the linen basket which stood near the wash basin and glanced in. "He seems to have come in here for a collar lately."

Bill peered in. There was one collar at the bottom of the basket.

"Yes. I daresay he would," he agreed. "If he suddenly found that the one he was wearing was uncomfortable or a little bit dirty, or something. He was very finicking."

Antony leant over and picked it out.

"It must have been uncomfortable this time," he said, after examining it carefully. "It couldn't very well be cleaner." He dropped it back again. "Anyway, he did come in here sometimes?"

"Oh, yes, rather."

"Yes, but what did Cayley come in for so secretly?"

"What did he want to shut the door for?" said Bill. "That's what I don't understand. You couldn't have seen him, anyhow."

"No. So it follows that I might have heard him. He was going to do something which he didn't want me to hear."

"By Jove, that's it!" said Bill eagerly.

"Yes; but what?"

Bill frowned hopefully to himself, but no inspiration came.

"Well, let's have some air, anyway," he said at last, exhausted by the effort, and he went to the window, opened it, and looked out. Then, struck by an idea, he turned back to Antony and said, "Do you think I had better go up to the pond to make sure that they're still at it? Because-"

He broke off suddenly at the sight of Antony's face.

"Oh, idiot, idiot!" Antony cried. "Oh, most super-excellent of Watsons! Oh, you lamb, you blessing! Oh, Gillingham, you incomparable a.s.s!"

"What on earth-"

"The window, the window!" cried Antony, pointing to it.

Bill turned back to the window, expecting it to say something. As it said nothing, he looked at Antony again.

"He was opening the window!" cried Antony.

"Who?"

"Cayley, of course." Very gravely and slowly he expounded. "He came in here in order to open the window. He shut the door so that I shouldn't hear him open the window. He opened the window. I came in here and found the window open. I said, 'This window is open. My amazing powers of a.n.a.lysis tell me that the murderer must have escaped by this window.' 'Oh,' said Cayley, raising his eyebrows. 'Well,' said he, 'I suppose you must be right.' Said I proudly, 'I am. For the window is open,' I said. Oh, you incomparable a.s.s!"

He understood now. It explained so much that had been puzzling him.

He tried to put himself in Cayley's place-Cayley, when Antony had first discovered him, hammering at the door and crying, "Let me in!" Whatever had happened inside the office, whoever had killed Robert, Cayley knew all about it, and knew that Mark was not inside, and had not escaped by the window. But it was necessary to Cayley's plans-to Mark's plans if they were acting in concert-that he should be thought so to have escaped. At some time, then, while he was hammering (the key in his pocket) at the locked door, he must suddenly have remembered-with what a shock!-that a mistake had been made. A window had not been left open!

Probably it would just have been a horrible doubt at first. Was the office window open? Surely it was open! Was it?.... Would he have time now to unlock the door, slip in, open the French windows and slip out again? No. At any moment the servants might come. It was too risky. Fatal, if he were discovered. But servants were stupid. He could get the windows safely open while they were crowding round the body. They wouldn't notice. He could do it somehow.