Arnold walked on.  Suddenly his attention was arrested.  Isaac was leaning over the banister of the landing above.

“Stop!”

Arnold paused for a moment.

“What is it?” he asked.

Isaac came swiftly down.  He brushed his cloth hat further back on his head as though it obscured his vision.  With both hands he gripped Arnold’s arm.

“Tell me,” he said, “what do you mean by that?”

“What I said,” Arnold answered; “but, for Heaven’s sake, don’t visit it on poor Ruth.  She told me that you had some printing-press in your room to set up your pamphlets, and that the tap, tap at night had kept her awake.  It’s no concern of mine.  I don’t care what you do or what rubbish you print, but I can’t bear to see the little woman getting frailer and frailer, Isaac.”

“She told you that?” Isaac muttered.

“She told me that,” Arnold assented.  “What is there in it?”

Isaac looked at him for a moment with an intentness which was indescribable.  His black eyes seemed on fire with suspicion, with searchfulness.  At last he let go the arm which he was clutching, and turned away.

“All right,” he said.  “Ruth shouldn’t talk, that’s all.  I don’t want every one to know that I am reduced to printing my little sheet in my bedroom.  Good night!”

Arnold looked after him in surprise.  It was very seldom that Isaac vouchsafed any form of greeting or farewell.  And then the shock came.  Isaac’s companion, who had been leaning over the banisters, waiting for him, had loosened the muffler about his neck and opened his overcoat.  His features were now recognizable—­a pale face with deep-set eyes and prominent forehead, a narrow chin, and a mouth which seemed set in a perpetual snarl.  Arnold stood gazing up at him in rapt amazement.  He had seen that face but once before, yet there was no possibility of any mistake.  It seemed, indeed, as though the recognition were mutual, for the man above, with an angry cry, turned suddenly away, buttoning up his overcoat with feverish fingers.  He called out to Isaac—­a hurried sentence, in a language which was strange to Arnold.  There was a brief exchange of breathless words.  Arnold moved slowly away, but before he had reached the street Isaac’s hand was upon his shoulder.

“One moment!” Isaac panted.  “My friend would like to know why you looked at him like that?”

Arnold did not hesitate.

“Isaac,” he said, gravely, “no doubt I seemed surprised.  I have seen that man before, only a night or two ago.”

“Where?  When?” Isaac demanded.

“I saw him hanging around the house of my employer,” Arnold said firmly, “under very suspicious circumstances.  He was inquiring then for Mr. Rosario.  It was the night before Rosario was murdered.”

“What do you mean by that?” Isaac asked, hoarsely.

“You had better ask yourself what it means,” Arnold replied.  “For Ruth’s sake, Isaac, don’t have anything to do with that man.  I don’t know anything about him—­I don’t want to know anything about him.  I simply beg you, for Ruth’s sake, to keep out of trouble.”