"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 analysis 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 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 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.
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 chuckled 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 Inspector 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 twig 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 don't say that he never went into the office. In fact, he must have gone. Elsie heard him." He stopped and repeated slowly, "She heard him, at least she says she did. But if he was there, he came out again by the door."
"Well, but where does that lead you?"
"Where it led Mark. The passage."
"Do you mean that he's been hiding there all the time?" Antony was silent until Bill had repeated his question, and then with an effort he came out of his thoughts and answered him.
"I don't know. But look here. Here is a possible explanation. I don't know if it is the right one I don't know, Bill; I'm rather frightened. Frightened of what may have happened, of what may be going to happen. However, here is an explanation. See if you can find any fault with it."
With his legs stretched out and his hands deep in his pockets, he lay back on the garden-seat, looking up to the blue summer sky above him, and just as if he saw up there the events of yesterday being enacted over again, he described them slowly to Bill as they happened.
"We'll begin at the moment when Mark shoots Robert. Call it an accident; probably it was. Mark would say it was, anyhow. He is in a panic, naturally. But he doesn't lock the door and run away. For one thing, the key is on the outside of the door; for another, he is not, quite such a fool as that. But he is in a horrible position. He is known to be on bad terms with his brother; he has just uttered some foolish threat to him, which may possibly have been overheard. What is he to do? He does the natural thing, the thing which Mark would always do in such circumstances. He consults Cayley, the invaluable, inevitable Cayley.
"Cayley is just outside, Cayley must have heard the shot, Cayley will tell him what to do. He opens the door just as Cayley is coming to see what is the matter. He explains rapidly. 'What's to be done, Cay? what's to be done? It was an accident. I swear it was an accident. He threatened me. He would have shot me if I hadn't. Think of something, quick!'
"Cayley has thought of something. 'Leave it to me,' he says. 'You clear out altogether. I shot him, if you like. I'll do all the explaining. Get away. Hide. Nobody saw you go in. Into the passage, quick. I'll come to you there as soon as I can.'
"Good Cayley. Faithful Cayley! Mark's courage comes back. Cayley will explain all right. Cayley will tell the servants that it was an accident. He will ring up the police. Nobody will suspect Cayley — Cayley has no quarrel with Robert. And then Cayley will come into the passage and tell him that it is all right, and Mark will go out by the other end, and saunter slowly back to the house. He will be told the news by one of the servants. Robert accidentally shot? Good Heavens!
"So, greatly reassured, Mark goes into the library. And Cayley goes to the door of the office…. and locks it. And then he bangs on the door and shouts, 'Let me in!'"
Antony was silent. Bill looked at him and shook his head.
"Yes, Tony, but that doesn't make sense. What's the point of Cayley behaving like that?"
Antony shrugged his shoulders without answering.
"And what has happened to Mark since?"
Antony shrugged his shoulders again.
"Well, the sooner we go into that passage, the better," said Bill.
"You're ready to go?"
"Quite," said Bill, surprised.
"You're quite ready for what we may find?"
"You're being dashed mysterious, old boy."
"I know I am." He gave a little laugh, and went on, "Perhaps I'm being an ass, just a melodramatic ass. Well, I hope I am." He looked at his watch.
"It's safe, is it? They're still busy at the pond?"
"We'd better make certain. Could you be a sleuthhound, Bill — one of those that travel on their stomachs very noiselessly? I mean, could you get near enough to the pond to make sure that Cayley is still there, without letting him see you?"