“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.”

“He also knew something else,” went on Antony.  “He knew that Robert was bound to betray his real character to you as soon as you met him.  He couldn’t pass him off on you as just a travelled brother from the Dominions, with perhaps a bit of an accent; he had to tell you at once, because you were bound to find out, that Robert was a wastrel.”

“Yes.  That’s sound enough.”

“Well, now, doesn’t it strike you that Mark made up his mind about all that rather quickly?”

“How do you mean?”

“He got this letter at breakfast.  He read it; and directly he had read it he began to confide in you all.  That is to say, in about one second he thought out the whole business and came to a decision—­to two decisions.  He considered the possibility of getting Robert out of the way before you came back, and decided that it was impossible.  He considered the possibility of Robert’s behaving like an ordinary decent person in public, and decided that it was very unlikely.  He came to those two decisions instantaneously, as he was reading the letter.  Isn’t that rather quick work?”

“Well, what’s the explanation?”

Antony waited until he had refilled and lighted his pipe before answering.

“What’s the explanation?  Well, let’s leave it for a moment and take another look at the two brothers.  In conjunction, this time, with Mrs. Norbury.”

“Mrs. Norbury?” said Bill, surprised.

“Yes.  Mark hoped to marry Miss Norbury.  Now, if Robert really was a blot upon the family honour, Mark would want to do one of two things.  Either keep it from the Norburys altogether, or else, if it had to come out, tell them himself before the news came to them indirectly.  Well, he told them.  But the funny thing is that he told them the day before Robert’s letter came.  Robert came, and was killed, the day before yesterday—­Tuesday.  Mark told Mrs. Norbury about him on Monday.  What do you make of that?”

“Coincidence,” said Bill, after careful thought.  “He’d always meant to tell her; his suit was prospering, and just before it was finally settled, he told her.  That happened to be Monday.  On Tuesday he got Robert’s letter, and felt jolly glad that he’d told her in time.”

“Well, it might be that, but it’s rather a curious coincidence.  And here is something which makes it very curious indeed.  It only occurred to me in the bath this morning.  Inspiring place, a bathroom.  Well, it’s this—­he told her on Monday morning, on his way to Middleston in the car.”