“We don’t know anything of the sort,” protested Bill. “We know for the purposes of our search. Obviously we can’t go tailing into Cayley’s bedroom and tapping his wardrobes; and obviously, therefore, if we are going to look for it at all, we must assume that it doesn’t begin there.” “Oh, I see.” Bill chewed a piece of grass thoughtfully. “Anyhow, it wouldn’t begin on an upstairs floor, would it?” “Probably not. Well, we’re getting on.” “You can wash out the kitchen and all that part of the house,” said Bill, after more thought. “We can’t go there.” “Right. And the cellars, if there are any.” “Well, that doesn’t leave us much.” “No. Of course it’s only a hundred-to-one chance that we find it, but what we want to consider is which is the most likely place of the few places in which we can look safely.” “All it amounts to,” said Bill, “is the living-rooms downstairs—dining-room, library, hall, billiard-room and the office rooms.” “Yes, that’s all.” “Well, the office is the most likely, isn’t it?” “Yes. Except for one thing.” “What’s that?” “Well, it’s on the wrong side of the house. One would expect the passage to start from the nearest place to which it is going. Why make it longer by going under the house first?” “Yes, that’s true. Well, then, you think the dining-room or the library?” “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.