“Yes.  And the library for choice.  I mean for our choice.  There are always servants going into dining-rooms.  We shouldn’t have much of a chance of exploring properly in there.  Besides, there’s another thing to remember.  Mark has kept this a secret for a year.  Could he have kept it a secret in the dining-room?  Could Miss Norris have got into the dining-room and used the secret door just after dinner without being seen?  It would have been much too risky.”

Bill got up eagerly.

“Come along,” he said, “let’s try the library.  If Cayley comes in, we can always pretend we’re choosing a book.”

Antony got up slowly, took his arm and walked back to the house with him.

The library was worth going into, passages or no passages.  Antony could never resist another person’s bookshelves.  As soon as he went into the room, he found himself wandering round it to see what books the owner read, or (more likely) did not read, but kept for the air which they lent to the house.  Mark had prided himself on his library.  It was a mixed collection of books.  Books which he had inherited both from his father and from his patron; books which he had bought because he was interested in them or, if not in them, in the authors to whom he wished to lend his patronage; books which he had ordered in beautifully bound editions, partly because they looked well on his shelves, lending a noble colour to his rooms, partly because no man of culture should ever be without them; old editions, new editions, expensive books, cheap books, a library in which everybody, whatever his taste, could be sure of finding something to suit him.

“And which is your particular fancy, Bill?” said Antony, looking from one shelf to another.  “Or are you always playing billiards?”

“I have a look at ‘Badminton’ sometimes,” said Bill.

“It’s over in that corner there.”  He waved a hand.

“Over here?” said Antony, going to it.

“Yes.”  He corrected himself suddenly.—­“Oh, no, it’s not.  It’s over there on the right now.  Mark had a grand re-arrangement of his library about a year ago.  It took him more than a week, he told us.  He’s got such a frightful lot, hasn’t he?”

“Now that’s very interesting,” said Antony, and he sat down and filled his pipe again.

There was indeed a “frightful lot” of books.  The four walls of the library were plastered with them from floor to ceiling, save only where the door and the two windows insisted on living their own life, even though an illiterate one.  To Bill it seemed the most hopeless room of any in which to look for a secret opening.

“We shall have to take every blessed book down,” he said, “before we can be certain that we haven’t missed it.”

“Anyway,” said Antony, “if we take them down one at a time, nobody can suspect us of sinister designs.  After all, what does one go into a library for, except to take books down?”