"That it was Cayley's idea to drag the pond."

"Oh! Oh, I say!" Bill was rather excited again. "You mean that he's hidden something there? Some false clue which he wants the police to find?"

"I hope so," said Antony earnestly, "but I'm afraid-" He stopped short.

"Afraid of what?"

"Afraid that he hasn't hidden anything there. Afraid that-"

"Well?"

"What's the safest place in which to hide anything very important?"

"Somewhere where n.o.body will look."

"There's a better place than that."

"What?"

"Somewhere where everybody has already looked."

"By Jove! You mean that as soon as the pond has been dragged, Cayley will hide something there?"

"Yes, I'm afraid so."

"But why afraid?"

"Because I think that it must be something very important, something which couldn't easily be hidden anywhere else."

"What?" asked Bill eagerly.

Antony shook his head.

"No, I'm not going to talk about it yet. We can wait and see what the Inspector finds. He may find something-I don't know what-something that Cayley has put there for him to find. But if he doesn't, then it will be because Cayley is going to hide something there to-night."

"What?" asked Bill again.

"You will see what, Bill," said Antony; "because we shall be there."

"Are we going to watch him?"

"Yes, if the Inspector finds nothing."

"That's good," said Bill.

If it were a question of Cayley or the Law, he was quite decided as to which side he was taking. Previous to the tragedy of yesterday he had got on well enough with both of the cousins, without being in the least intimate with either. Indeed, of the two he preferred, perhaps, the silent, solid Cayley to the more volatile Mark. Cayley's qualities, as they appeared to Bill, may have been chiefly negative; but even if this merit lay in the fact that he never exposed whatever weaknesses he may have had, this is an excellent quality in a fellow-guest (or, if you like, fellow-host) in a house where one is continually visiting. Mark's weaknesses, on the other hand, were very plain to the eye, and Bill had seen a good deal of them.

Yet, though he had hesitated to define his position that morning in regard to Mark, he did not hesitate to place himself on the side of the Law against Cayley. Mark, after all, had done him no harm, but Cayley had committed an unforgivable offence. Cayley had listened secretly to a private conversation between himself and Tony. Let Cayley hang, if the Law demanded it.

Antony looked at his watch and stood up.

"Come along," he said. "It's time for that job I spoke about."

"The pa.s.sage?" said Bill eagerly.

"No; the thing which I said that I had to do this afternoon."

"Oh, of course. What is it?"

Without saying anything, Antony led the way indoors to the office.

It was three o'clock, and at three o'clock yesterday Antony and Cayley had found the body. At a few minutes after three, he had been looking out of the window of the adjoining room, and had been surprised suddenly to find the door open and Cayley behind him. He had vaguely wondered at the time why he had expected the door to be shut, but he had had no time then to worry the thing out, and he had promised himself to look into it at his leisure afterwards. Possibly it meant nothing; possibly, if it meant anything, he could have found out its meaning by a visit to the office that morning. But he had felt that he would be more likely to recapture the impressions of yesterday if he chose as far as possible the same conditions for his experiment. So he had decided that three o'clock that afternoon should find him once more in the office.

As he went into the room, followed by Bill, he felt it almost as a shock that there was now no body of Robert lying there between the two doors. But there was a dark stain which showed where the dead man's head had been, and Antony knelt down over it, as he had knelt twenty-four hours before.

"I want to go through it again," he said. "You must be Cayley. Cayley said he would get some water. I remember thinking that water wasn't much good to a dead man, and that probably he was only too glad to do anything rather than nothing. He came back with a wet sponge and a handkerchief. I suppose he got the handkerchief from the chest of drawers. Wait a bit."

He got up and went into the adjoining room; looked round it, pulled open a drawer or two, and, after shutting all the doors, came back to the office.

"The sponge is there, and there are handkerchiefs in the top right-hand drawer. Now then, Bill, just pretend you're Cayley. You've just said something about water, and you get up."

Feeling that it was all a little uncanny, Bill, who had been kneeling beside his friend, got up and walked out. Antony, as he had done on the previous day, looked up after him as he went. Bill turned into the room on the right, opened the drawer and got the handkerchief, damped the sponge and came back.

"Well?" he said wonderingly.

Antony shook his head.

"It's all different," he said. "For one thing, you made a devil of a noise and Cayley didn't."

"Perhaps you weren't listening when Cayley went in?"

"I wasn't. But I should have heard him if I could have heard him, and I should have remembered afterwards."

"Perhaps Cayley shut the door after him."

"Wait!"

He pressed his hand over his eyes and thought. It wasn't anything which he had heard, but something which he had seen. He tried desperately hard to see it again.... He saw Cayley getting up, opening the door from the office, leaving it open and walking into the pa.s.sage, turning to the door on the right, opening it, going in, and then-What did his eyes see after that? If they would only tell him again!

Suddenly he jumped up, his face alight. "Bill, I've got it!" he cried.

"What?"

"The shadow on the wall! I was looking at the shadow on the wall. Oh, a.s.s, and ten times a.s.s!"

Bill looked uncomprehendingly at him. Antony took his arm and pointed to the wall of the pa.s.sage.

"Look at the sunlight on it," he said. "That's because you've left the door of that room open. The sun comes straight in through the windows. Now, I'm going to shut the door. Look! D'you see how the shadow moves across? That's what I saw the shadow moving across as the door shut behind him. Bill, go in and shut the door behind you quite naturally. Quick!"