"Go on," said Bill eagerly.
"Well, I felt pretty sure about that, and I wanted an explanation of it. Why had Mark changed down there instead of in his bedroom? The only answer was that the fact of his changing had to be kept secret. When did he change? The only possible time was between lunch (when he would be seen by the servants) and the moment of Robert's arrival. And when did Cayley collect the clothes in a bundle? Again, the only answer was 'Before Robert's arrival.' So another x was wanted—to fit those three conditions."
"And the answer was that a murder was intended, even before Robert arrived?"
"Yes. Well now, it couldn't be intended on the strength of that letter, unless there was very much more behind the letter than we knew. Nor was it possible a murder could be intended without any more preparation than the changing into a different suit in which to escape. The thing was too childish. Also, if Robert was to be murdered, why go out of the way to announce his existence to you all—even, at the cost of some trouble, to Mrs. Norbury? What did it all mean? I didn't know. But I began to feel now that Robert was an incident only; that the plot was a plot of Cayley's against Mark—either to get him to kill his brother, or to get his brother to kill him—and that for some inexplicable reason Mark seemed to be lending himself to the plot." He was silent for a little, and then said, almost to himself, "
