He descended the stairs again, to return in a minute or so and announce that another street could be reached through the back of the house. There and then they settled the plan of campaign. One at a time they would go to the hotel for their meals, so that the door would never be unwatched throughout the day. Dr. Cairn determined to make no inquiries respecting the house, as this might put the enemy upon his guard. "We are in his own country, Rob," he said. "Here, we can trust no one." Thereupon they commenced their singular and self-imposed task. In turn they went back to the hotel for breakfast, and watched fruitlessly throughout the morning. They lunched in the same way, and throughout the great midday heat sat hidden in the ruined building, mounting guard over that iron-studded door. It was a dreary and monotonous day, long to be remembered by both of them, and when the hour of sunset drew nigh, and their vigil remained unrewarded, they began to doubt the wisdom of their tactics. The street was but little frequented; there was not the slightest chance of their presence being discovered. It was very quiet, too, so that no one could have approached unheard. At the hotel they had learnt the cause of the explosion during the night; an accident in the engine-room of a tramp steamer, which had done considerable damage, but caused no bodily injury. "We may hope to win yet," said Dr. Cairn, in speaking of the incident. "It was the hand of God." Silence had prevailed between them for a long time, and he was about to propose that his son should go back to dinner, when the rare sound of a footstep below checked the words upon his lips. Both craned their necks to obtain a view of the pedestrian. An old man stooping beneath the burden of years and resting much of his weight upon a staff, came tottering into sight. The watchers crouched back, breathless with excitement, as the newcomer paused before the iron-studded door, and from beneath his cloak took out a big key. Inserting it into the lock, he swung open the door; it creaked upon ancient hinges as it opened inward, revealing a glimpse of a stone floor. As the old man entered, Dr. Cairn grasped his son by the wrist. "Down!" he whispered. "Now is our chance!" They ran down the rickety stairs, crossed the narrow street, and Robert Cairn cautiously looked in around the door which had been left ajar. Black against the dim light of another door at the further end of the large and barn-like apartment, showed the stooping figure. Tap, tap, tap! went the stick; and the old man had disappeared around a corner. "Where can we hide?" whispered Dr. Cairn. "He is evidently making a tour of inspection." The sound of footsteps mounting to the upper apartments came to their ears. They looked about them right and left, and presently the younger man detected a large wooden cupboard set in one wall. Opening it, he saw that it contained but one shelf only, near the top.