"We might not be able to hear them," answered the lieutenant, even against his own judgment. "But look at it this way. Even though they never were inside here, they had a fair idea of what the place was like. They knew from that that we needed help, and needed it quickly. If one went alone, and anything happened to him on the way, the other might wait here indefinitely, not knowing whether he had got assistance or not. By going together they took the safest course." And Lieutenant Mackinson's reasoning was correct. That was exactly the way Joe and Frank had figured it out, and, the latter forgetting all about his own wound, they had started as fast as they could for the American front. "Keep cool, conserve your energy, and I feel certain everything will be all right," the lieutenant told the two friends with whom, in such a short time, he already had gone through so many harrowing experiences. At that very same moment, a quarter of a mile away, Joe brought his companion to a halt, took out his flashlight, and, facing the American line, began making and breaking the connection in a way to give a number of short, even flashes. Presently a light appeared, was extinguished and appeared again, at the edge of the American-French lines. Joe had resorted to another sort of wireless--the "blinker"--and, not knowing the call signal for the station he was nearest, had given the prescribed call in such a case, a series of short flashes, or dots. The station had acknowledged, and he began sending his message out of the little battery in his hand: "Americans. Three of party caught in cave-in. Need help." And the answer was flashed back in the same code: "Approach. Keep light on. Countersign." Following these instructions, with Joe in the lead with the flashlight held out in front of him, they dashed on to the trenches. They gasped out the countersign, and were escorted by a sentry to the quarters of the officer of that particular section. In a few words they told him what had happened. Without an instant's delay the latter, a colonel of artillery, reached for his telephone. "Ask Captain Hallowell to come here immediately," he said, and severed the connection. He seemed already to have decided upon some sort of a plan, and his decisive manner gave the two lads a feeling of confidence in him. He reached into a drawer of his desk and drew out a large map. He ran his fingers across it and then came to a stop at a little black dot which appeared just in the angle of two converging red lines. "Is that it?" he asked, turning to Jerry and Frank. They examined the map carefully for a moment and then told him that it was. Just then Captain Hallowell entered. His boots were spattered with mud, his face was grimy, and his eyes were bloodshot, indicating that he had been for many hours without sleep.