As she commenced to translate the tissue paper messages in a low, tremulous voice, the sound of a door being closed and locked in the room overhead silenced her. The next instant she had stepped out to the stairs and called: "Karl!" There was no reply. Smith came out to the stair-well and listened. "It is his custom," she whispered, "to lock his door before retiring. That is what we heard." "Call again." "He can’t hear me. He is in bed." "Call, all the same." "Karl!" she cried out in an unsteady voice. CHAPTER XXIII MADAM DEATH There was no reply, because the young man was hanging out over his window sill in the darkness trying to switch away, from her closed window below, the big, clattering Death’s Head moth which obstinately and persistently fluttered there. What possessed the moth to continue battering its wings at the window of the room below? Had the other moths which he released done so, too? They had darted out of his room into the night, each garnished with a tissue robe. He supposed they had flown north; he had not looked out to see. What had gone wrong with this moth, then? He took his emaciated blond head between his bony fingers and pondered, probing for reason with German thoroughness--that celebrated thoroughness which is invariably riddled with flaws. Of all contingencies he had thought--or so it seemed to him. He could not recollect any precaution neglected. He had come to Sainte Lesse for a clearly defined object and to make certain reports concerning matters of interest to the German military authorities north of Nivelle. The idea, inspired by the experiments of Henri Fabre, was original with him. Patiently, during the previous year, he had worked it out--had proved his theory by a series of experiments with moths of this species. He had arranged with his staff comrade, Dr. Glück, for a forced hatching of the pupæ which the latter had patiently bred from the enormous green and violet-banded caterpillars. At least one female Death’s Head must be ready, caged in the trenches beyond Nivelle. Hundreds of pupæ could not have died. Where, then, was his error--if, indeed, he had made any? Leaning from the window, he looked down at the frantic moth, perplexed, a little uneasy now. "Swine!" he muttered. "What, then, ails you that you do not fly to the mistress awaiting you over yonder?" He could see the cylinder of white tissue shining on the creature’s body, where it fluttered against the pane, illuminated by the rays of the candle from within the young girl’s room. Could it be possible that the candle-light was proving the greater attraction? Even as the possibility entered his mind, he saw another Death’s Head dart at the window below and join the first one. But this newcomer wore no tissue jacket. Then, out of the darkness the Death’s Heads began to come to the window below, swarms of them, startling him with the racket of their wings.