"Hush!" the girl said softly, and in excitement. "He may hear you! He’s very quick!" But the strange occupant of the house had already ascended out of view, and a few moments later they heard a click as he put his key into the Yale lock of the closed room. They distinctly heard him open the door, and as distinctly heard him close it again. "You wait here, Marigold," the young fellow whispered. "I’ll creep up and see what I can. Perhaps I shall hear them talking." "Yes, do," she said. "But take the greatest care. Mind the stairs don’t creak. He’ll be alarmed in a moment." "Leave that to me," he replied, and next moment he left her side, and slowly ascending the few remaining steps, gained the hall, and then the foot of the stairs which led to the first floor. Though he had not removed his shoes he made no noise, for he trod slowly and cautiously, never lifting one foot until the other was down silently. Thus very slowly he followed the mysterious man in white. Hardly had he ascended four steps when an electric bell sounded, apparently in the locked room. He halted, and in an instant decided to retreat. Scarcely before Marigold had realised that the alarm had sounded, he sprang down, rejoined her, and whispering: "Quick! Let’s get down!" he descended into the dark kitchen. There, clutching her by the arm, he felt his way to the door. Without pausing to listen to the effect of the alarm upon the man upstairs, the pair passed out into the area, closed the door after them, hurried up the steps, and out into the street. "Let’s get away before he sees us!" Gerald urged, and they both ran light-footed along to the corner into King Street, where they escaped. "There’s a trap in that house!" Durrant declared, as after hurrying breathlessly they walked along in the direction of the Broadway Station. "Upon one of those stairs is an electrical contact which gives to the locked room the alarm of an intruder. He switched it on from his room below!" "Yes!" said the girl. "I feel sure there is." "And that shows that there’s something very wrong somewhere. Mr. Boyne has, in secret, a guest who is in hiding upstairs. He takes him food and water every night—as we have seen with our own eyes. And, further, he had taken the precaution of installing an electrical alarm in case anyone followed him upstairs while he was there with his friend." "True," said the girl. "But why does he disguise himself whenever he goes up there?" "That we cannot yet tell. At present it is a complete mystery." "And a most uncanny one!" "It is, I can’t see the motive of that disguise." "Is it not weird? He was covered from head to foot in that white cloak, and only those two slits for his eyes." "Yes. And he moved as silently as a shadow." So the pair conversed until they reached the Broadway Station, and left by the Underground a few moments later. What they had witnessed that night had increased the mystery a hundredfold.