"Yes."

"We know that he announced his approaching arrival to Mark in a
rather unpleasant letter, which I have in my pocket."

"Yes."

"And then we know rather a curious thing. We know that Mark told
you all that this black sheep was coming. Now, why did he tell
you?"

Bill was thoughtful for a moment.

"I suppose," he said slowly, "that he knew we were bound to see
him, and thought that the best way was to be quite frank about
him."

"But were you bound to see him? You were all away playing golf."

"We were bound to see him if he stayed in the house that night."

"Very well, then. That's one thing we've discovered. Mark knew
that Robert was staying in the house that night. Or shall we put
it this way--he knew that there was no chance of getting Robert
out of the house at once."

Bill looked at his friend eagerly.

"Go on," he said. "This is getting interesting."