Well, not quite alone.  There was a sudden voice in the hall outside.

“Good Lord!” said Bill, turning round with a start, “Cayley!”

If he was not so quick in thought as Antony, he was quick enough in action.  Thought was not demanded now.  To close the secret door safely but noiselessly, to make sure that the books were in the right places, to move away to another row of shelves so as to be discovered deep in “Badminton” or “Baedeker” or whomever the kind gods should send to his aid the difficulty was not to decide what to do, but to do all this in five seconds rather than in six.

“Ah, there you are,” said Cayley from the doorway.

“Hallo!” said Bill, in surprise, looking up from the fourth volume of “The Life and Works of Samuel Taylor Coleridge.”  “Have they finished?”

“Finished what?”

“The pond,” said Bill, wondering why he was reading Coleridge on such a fine afternoon.  Desperately he tried to think of a good reason .... verifying a quotation—­an argument with Antony—­that would do.  But what quotation?

“Oh, no.  They’re still at it.  Where’s Gillingham?”

’The Ancient Mariner’—­water, water, everywhere—­or was that something else?  And where was Gillingham?  Water, water everywhere . . .

“Tony?  Oh, he’s about somewhere.  We’re just going down to the village.  They aren’t finding anything at the pond, are they?”

“No.  But they like doing it.  Something off their minds when they can say they’ve done it.”

Bill, deep in his book, looked up and said “Yes,” and went back to it again.  He was just getting to the place.

“What’s the book?” said Cayley, coming up to him.  Out of the corner of his eye he glanced at the shelf of sermons as he came.  Bill saw that glance and wondered.  Was there anything there to give away the secret?

“I was just looking up a quotation,” he drawled.  “Tony and I had a bet about it.  You know that thing about—­er water, water everywhere, and—­er—­not a drop to drink.” (But what on earth, he wondered to himself, were they betting about?)

“‘Nor any drop to drink,’ to be accurate.”

Bill looked at him in surprise.  Then a happy smile came on his face.

“Quite sure?” he said.

“Of course.”

“Then you’ve saved me a lot of trouble.  That’s, what the bet was about.”  He closed the book with a slam, put it back in its shelf, and began to feel for his pipe and tobacco.  “I was a fool to bet with Tony,” he added.  “He always knows that sort of thing.”

So far, so good.  But here was Cayley still in the library, and there was Antony, all unsuspecting, in the passage.  When Antony came back he would not be surprised to find the door closed, because the whole object of his going had been to see if he could open it easily from the inside.  At any moment, then, the bookshelf might swing back and show Antony’s head in the gap.  A nice surprise for Cayley!