Three times did Joe drop to the ground, as a shadow seemed to move somewhere out in the distance before him. But each time he was up and off again almost upon the instant, thinking of his own safety only as that of his three friends depended upon it. And what of those inside? Even the courageous Lieutenant Mackinson was beginning to show the anxiety he felt, while Jerry and Slim, despite their bravest efforts, gave way to occasional expressions of the horror of the thing. They had pounded upon the walls until they had been overcome with despair, and then they had set to work digging with the only instruments at hand--the bayonets on the German rifles. But soon they realized that this, too, was as hopeless as the pounding, for it further exhausted the energy which the foul air was rapidly sapping, without making any apparent opening in the thick earthen wall that surrounded them. "Well," said Slim at last, gulping back his nausea, and smiling almost in his old time way, "I'm as anxious as anybody to keep up hope to the last. But if this is to be our end, I guess we can face it as Americans should." "Bravo!" exclaimed Lieutenant Mackinson, "I always knew that each one of you fellows had the right sort of stuff in you." And Jerry, too, slapped him affectionately on the back. "Slim," he said, smiling over at his chum, and ready for his pun, even under such circumstances, "my head is feeling a 'trifle heavy,' but I'm game to stand up to the last." Thus they sat down to wait--for just what, they did not know--while at that very moment, four feet away from them on the other side of the wall, faithful Joe was setting up the flashlight exactly according to directions. For a few seconds he waited, and then, three times in quick succession, a rocket went into the air from just behind the American lines. Over there Captain Hallowell himself found the range, submitted it to his most expert gunner, who verified it, and then they waited for the three minutes to elapse, during which Joe was to seek a place of safety. It was in that interval, too, that Fate intervened for those within the cave, for they were sitting with their backs to the very point against which the shell was to be directed. "We need all our strength," Lieutenant Mackinson was saying. "So long as possible we want to remain in full possession of our senses. The air is purer near the floor. I think it would be better to lie down." And following his suggestion and example, the other two stretched themselves out in the middle of the cavern. Within the American lines, at that point where a regiment of heavy artillery was stationed, Captain Hallowell raised his hand in signal to his gunner. Out on the parapet of the front trench an anxious colonel was standing, regardless of all danger, a pair of powerful glasses to his eyes. His vision was focused upon a little light far out in No Man's Land.