He explained his reasons for thinking that the secret of the passage was concerned in some way with the secret of Robert’s death, and went on: “My theory is that Mark discovered the passage about a year ago—the time when he began to get keen on croquet. The passage came out into the floor of the shed, and probably it was Cayley’s idea to put a croquet-box over the trap-door, so as to hide it more completely. You know, when once you’ve discovered a secret yourself, it always seems as if it must be so obvious to everybody else. I can imagine that Mark loved having this little secret all to himself—and to Cayley, of course, but Cayley wouldn’t count—and they must have had great fun fixing it up, and making it more difficult for other people to find out. Well then, when Miss Norris was going to dress-up, Cayley gave it away. Probably he told her that she could never get down to the bowling-green without being discovered, and then perhaps showed that he knew there was one way in which she could do it, and she wormed the secret out of him somehow.” “But this was two or three days before Robert turned up.” “Exactly. I am not suggesting that there was anything sinister about the passage in the first place. It was just a little private bit of romance and adventure for Mark, three days ago. He didn’t even know that Robert was coming. But somehow the passage has been used since, in connection with Robert. Perhaps Mark escaped that way; perhaps he’s hiding there now. And if so, then the only person who could give him away was Miss Norris. And she of course would only do it innocently—not knowing that the passage had anything to do with it.” “So it was safer to have her out of the way?” “Yes.” “But, look here, Tony, why do you want to bother about _this_ end of it? We can always get in at the bowling-green end.” “I know, but if we do that we shall have to do it openly. It will mean breaking open the box, and letting Cayley know that we’ve done it. You see, Bill, if we don’t find anything out for ourselves in the next day or two, we’ve got to tell the police what we _have_ found out, and then they can explore the passage for themselves. But I don’t want to do that yet.” “Rather not.” “So we’ve got to carry on secretly for a bit. It’s the only way.” He smiled and added, “And it’s much more fun.” “Rather!” Bill chuckled to himself. “Very well. Where does the secret passage begin?” CHAPTER XI. The Reverend Theodore Ussher “There’s one thing, which we have got to realize at once,” said Antony, “and that is that if we don’t find it easily, we shan’t find it at all.” “You mean that we shan’t have time?” “Neither time nor opportunity. Which is rather a consoling thought to a lazy person like me.” “But it makes it much harder, if we can’t really look properly.” “Harder to find, yes, but so much easier to look. For instance, the passage might begin in Cayley’s bedroom. Well, now we know that it doesn’t.”