He lay back on the divan, languidly lighting another cigarette.  Graham beckoned Robinson.  Bobby followed them out, suspecting Graham’s purpose, unwilling that action should be taken too hastily against the Panamanian; for even now guilty knowledge seemed incompatible with Paredes’s polished reserve.  When he joined the others, indeed, Graham with an aggressive air was demanding the district attorney’s intentions.

“If he could elude you so easily last night, it’s common sense to put him where you can find him in case of need.  He’s given you excuse enough.”

“The man’s got me guessing,” Robinson mused, “but there are other elements.”

“What’s happened since we left?” Graham asked quickly.  “Have you got any trace of Howells’s evidence?”

Robinson smiled enigmatically, but his failure was apparent.

“I’m like Howells,” he said.  “I’d risk nearly anything myself to learn how the room was entered, how the crimes were committed, how those poor devils were made to alter their positions.”

“So,” Bobby said, “you had my rooms in New York searched.  You had me followed to-day.  It’s ridiculous.”

Robinson ignored him.  He stepped to the front door, opened it, and looked around the court.

“What did the sphinx mean about ghosts in the court?”

They walked out, gazing helplessly at the trampled grass about the fountain, at the melancholy walls, at the partly opened window of the room of mystery.

“He knows something,” Robinson mused.  “Maybe you’re right, Mr. Graham, but I wonder if I oughtn’t to go farther and take you all.”

Graham smiled uncomfortably, but Bobby knew why the official failed to follow that radical course.  Like Howells, he hesitated to remove from the Cedars the person most likely to solve its mystery.  As long as a chance remained that Howells had been right about Bobby he would give Silas Blackburn’s grandson his head, merely making sure, as he had done this morning, that there should be no escape.  He glanced up.

“I wonder if our foreigner’s laughing at me now.”

Graham made a movement toward the door.

“We might,” he said significantly, “find that out without disturbing him.”

Robinson nodded and led the way silently back to the house.  Such a method was repugnant to Bobby, and he followed at a distance.  Then he saw from the movements of the two men ahead that the library had again offered the unexpected, and he entered.  Paredes was no longer in the room.  Bobby was about to speak, but Robinson shook his head angrily, raising his hand in a gesture of warning.  All three strained forward, listening, and Bobby caught the sound that had arrested the others—­a stealthy scraping that would have been inaudible except through such a brooding silence as pervaded the old house.