"If we bump a mine," said Frank, "I can't see that it will make any difference whether we are going fast or slowly." "It won't make much," agreed Jack dryly. According to Lord Hastings' calculations, which proved to be correct, they were now off the coast of Holland. Several hours passed, and then, at Lord Hastings' command, the solid glass front of the submarine was plunged into utter darkness and the powerful searchlight brought to bear on the water ahead, while, at the same time, the speed was reduced to seven knots. In spite of its powerfulness, the searchlight lighted up the water for only a short distance ahead, and, as Lord Hastings said, should a mine be seen ahead prompt action would be necessary to save them from disaster. Frank took his place just behind the searchlight, while the compartment behind was closed that no light might enter from without, thus adding a little to the effect of the searchlight. His watch was set for two hours, and he had sat most of that time with eyes straight ahead, when he became conscious that the door behind him was being pushed slowly open. Certain in his own mind that his watch was not up, and mindful of Lord Hastings' order that the door be not opened unless absolutely necessary, Frank nevertheless did not take his eyes off the sea ahead, but called out: "Who's there? What is it?" There was no answer. "Something wrong," muttered the lad to himself, and acted upon the instant. Through the little tube at his elbow he shouted a command: "Stop her!" At the same moment, even as he felt the sudden shock as the submarine paused abruptly in her pace, he sprang from his seat and turned toward the door, ready for anything with one hand on his automatic, for he felt sure that he was in danger. In the darkness behind he could see nothing, but the slight squeaking of a board gave evidence of another presence. Frank, with the searchlight behind, was in full view of the other, and the lad realized it. With a quick backward leap he snapped off the searchlight, and then dropped quickly to the floor, even as a figure rushed toward him in the darkness. Frank's ruse undoubtedly stood him to good advantage. A foot struck his prostrate body, and the figure of a man pitched over him, muttering a fierce imprecation as he fell to the floor. Before the latter could rise, Frank grappled with him. Quickly reversing his revolver, he brought the butt of the weapon down in the direction in which he judged the man's head to be. It struck something soft, and a guttural howl of pain went up. "A spy!" Frank found time to think to himself. But he had not struck the man's head, only a hand which had been outstretched, and before he could draw his pocket searchlight to ascertain what damage he had done, the lad felt a pair of arms about his neck, and a hand seeking to entwine itself in his throat.