“Rub it in,” Robinson grinned.  “I’ll take my medicine.”

They gathered closer about the Panamanian.  Jenkins sidled to the back of his chair.

“I don’t see how you found it out,” he muttered.

“I had only one advantage over you or the police, Graham,” Paredes began, “and you were in a position to overcome that.  Maria did telephone me the afternoon of that ghastly dinner.  She asked me to get hold of Bobby.  She was plainly anxious to keep him in New York that night, and, to be frank, I was glad enough to help her when you turned up, trying to impress us with your puritan watchfulness.  Even you guessed that she had drugged Bobby.  I suspected it when I saw him go to pieces in the cafe.  He gave me the slip, as I told you, in the coat room when I was trying to get him home, so I went back and asked Maria what her idea was.  She laughed in my face, denying everything.  I, too, suspected the stranger, but I’ve convinced myself that he simply happened along by chance.

“Now here’s the first significant point:  Maria by drugging Bobby defeated her own purpose.  He had been drinking more than the Band of Hope would approve of, and on top of that he got an overdose of a powerful drug.  The doctor can tell you better than I of the likely effect of such a combination.”

“What I told you in the court, Bobby,” the doctor answered, “much the same symptoms as genuine aphasia.  Your brain was unquestionably dulled by an overdose on top of all that alcohol, while your mechanical reflexes were stimulated.  Automatically you followed your ruling impulse.  Automatically at the last minute you revolted from exposing yourself in such a condition to your cousin and your grandfather.  Your lucid period in the woods just before you reached the deserted house and went to sleep showed that your exercise was overcoming the effect of the drug.  That moment, you’ll remember, was coloured by the fanciful ideas such a drug would induce.”

“So, Bobby,” Paredes said, “although you were asleep when the body moved and when Howells was murdered, you can be sure you weren’t anywhere near the old room.”

“But I walked in my sleep last night,” Bobby reminded him.

The doctor slapped his knee.

“I understand.  It was only when we thought that was your habit that it frightened us.  It’s plain.  This sleep-walking had been suggested to you and you had brooded upon the suggestion until you were bound to respond.  Graham’s presence in your room, watching for just that reaction, was a perpetual, an unescapable stimulation.  It would have been a miracle in itself if your brain had failed to carry it out.”

Bobby made a swift gesture of distaste.

“If you hadn’t come, Carlos, where would I have been?”

“Why did you come?” Graham asked.