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 outfit¹.”
 
“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 linen² 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, exhausted³ 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 blessing⁴! Oh, Gillingham, you incomparable ass⁵!”
 
“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 expounded⁶. “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 analysis tell me that the murderer must have escaped by this window.’ ‘Oh,’ said Cayley, raising his eyebrows⁷. ‘Well,’ said he, ‘I suppose you must be right.’ Said I proudly, ‘I am. For the window is open,’ I said. Oh, you incomparable ass!”
 
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 acting⁸ 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 risky⁹. 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.
 
And then Antony’s sudden appearance! Here was a complication. And Antony suggesting that they should try the window! Why, the window was just what he wanted to avoid. No wonder he had seemed dazed at first.
 
Ah, and here at last was the explanation why they had gone the longest way round and yet run. It was Cayley’s only chance of getting a start on Antony, of getting to the windows first, of working them open somehow before Antony caught him up. Even if that were impossible, he must get there first, just to make sure. Perhaps they were open. He must get away from Antony and see. And if they were shut, hopelessly shut, then he must have a moment to himself, a moment in which to think of some other plan, and avoid the ruin which seemed so suddenly to be threatening.
 
So he had run. But Antony had kept up with him. They had broken in the window together, and gone into the office. But Cayley was not done yet. There was the dressing-room window! But quietly, quietly. Antony mustn’t hear.
 
And Antony didn’t hear. Indeed, he had played up to Cayley splendidly. Not only had he called attention to the open window, but he had carefully explained to Cayley why Mark had chosen this particular window in preference to the office window. And Cayley had agreed that probably that was the reason. How he must have chuckled¹⁰ to himself! But he was still a little afraid. Afraid that Antony would examine the shrubbery. Why? Obviously because there was no trace of anyone having broken through the shrubbery. No doubt Cayley had provided the necessary traces since, and had helped the Inspector¹¹ to find them. Had he even gone as far as footmarks—in Mark’s shoes? But the ground was very hard. Perhaps footmarks were not necessary. Antony smiled as he thought of the big Cayley trying to squeeze into the dapper little Mark’s shoes. Cayley must have been glad that footmarks were not necessary.
 
No, the open window was enough; the open window and a broken twig¹² or two. But quietly, quietly. Antony mustn’t hear. And Antony had not heard.... But he had seen a shadow on the wall.
 
They were outside on the lawn again now, Bill and Antony, and Bill was listening open-mouthed to his friend’s theory of yesterday’s happenings. It fitted in, it explained things, but it did not get them any further. It only gave them another mystery to solve.
 
“What’s that?” said Antony.
 
“Mark. Where’s Mark? If he never went into the office at all, then where is he now?”
 
“I do............