“Let’s look at it from Cayley’s point of view,” said Antony.  “He may not know that we’re on his track, but he can’t help being suspicious of us.  He’s bound to be suspicious of everybody in the house, and more particularly of us, because we’re presumably more intelligent than the others.”

He stopped for a moment to light his pipe, and Bill took the opportunity of looking more intelligent than Mrs. Stevens.

“Now, he has got something to hide to-night, and he’s going to take good care that we aren’t watching him.  Well, what will he do?”

“See that we are asleep first, before he starts out.”

“Yes.  Come and tuck us up, and see that we’re nice and comfortable.”

“Yes, that’s awkward,” said Bill.  “But we could lock our doors, and then he wouldn’t know that we weren’t there.”

“Have you ever locked your door?”

“Never.”

“No.  And you can bet that Cayley knows that.  Anyway, he’d bang on it, and you wouldn’t answer, and then what would he think?”

Bill was silent; crushed.

“Then I don’t see how we’re going to do it,” he said, after deep thought.  “He’ll obviously come to us just before he starts out, and that doesn’t give us time to get to the pond in front of him.”

“Let’s put ourselves in his place,” said Antony, puffing slowly at his pipe.  “He’s got the body, or whatever it is, in the passage.  He won’t come up the stairs, carrying it in his arms, and look in at our doors to see if we’re awake.  He’ll have to make sure about us first, and then go down for the body afterwards.  So that gives us a little time.”

“Y-yes,” said Bill doubtfully.  “We might just do it, but it’ll be a bit of a rush.”

“But wait.  When he’s gone down to the passage and got the body, what will he do next?”

“Come out again,” said Bill helpfully.

“Yes; but which end?”

Bill sat up with a start.

“By Jove, you mean that he will go out at the far end by the bowling-green?”

“Don’t you think so?  Just imagine him walking across the lawn in full view of the house, at midnight, with a body in his arms.  Think of the awful feeling he would have in the back of the neck, wondering if anybody, any restless sleeper, had chosen just that moment to wander to the window and look out into the night.  There’s still plenty of moonlight, Bill.  Is he going to walk across the park in the moonlight, with all those windows staring at him?  Not if he can help it.  But he can get out by the bowling green, and then come to the pond without ever being in sight of the house, at all.”

“You’re right.  And that will just about give us time.  Good.  Now, what’s the next thing?”

“The next thing is to mark the exact place in the pond where he drops whatever he drops.”

“So that we can fish it out again.”

“If we can see what it is, we shan’t want to.  The police can have a go at it to-morrow.  But if it’s something we can’t identify from a distance, then we must try and get it out.  To see whether it’s worth telling the police about.”