"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
