"Captain," said the colonel bluntly, "these young men are of the Signal Corps, as you you can see. They were detailed to-night to establish an outpost wire communication to Hill No. 8. You know it?" "Very well, sir," the captain replied, his interest increasing. "Well," continued the colonel, "they got there all right. But the other three in the party had hardly entered that hole when the entrance caved in." "Great Scott!" ejaculated the captain. "I know that cavern. They can't last there long." "Exactly," affirmed the colonel. "What is your suggestion?" For a full moment Captain Hallowell was silent. "There is only one way," he said finally, "and that is a dangerous way. Blast them out." "Blast them out?" repeated the colonel, but apparently without surprise. "How?" "It would take too long to dig them out," Captain Hallowell answered. "And, besides, that could hardly be done without some sort of light, and that would attract enemy fire. There is but one chance, and that is to blast them out with one of our big guns!" "Can you do it?" the colonel demanded again, in his blunt, insistent way. "I will do my utmost to save them, sir," Captain Hallowell replied. "Very well, then," answered his superior officer. "If you feel certain that is the only way, go ahead. Personally, knowing the place as I do, I see no other method myself. Have you the range?" "I did have, sir," said Captain Hallowell, "but in such a delicate matter as this it would be necessary to be absolutely accurate. We have been firing practically all day, and the position of the guns changes slightly, of course. I would want to find a new and exact range." He had noticed Frank's limp arm, and he turned to Joe. "Take this flashlight," he ordered. "It is more powerful than yours. Get back there as quickly as you can, and follow to the letter these directions: Keep between us and that hill until you get to it. Stay on this side of the hill and crawl around toward the entrance until you get to a point where you can place this light, facing us, two feet above the ground and one foot in from the outer surface extremity. Leave it there until you see three quick successive rockets go straight up in the air from here. After that I will give you three minutes in which to get back to a place of safety. I'll put that flashlight out of business, and I think I can liberate your friends." "Is your injury a serious one?" the colonel demanded of Frank. "Very slight, sir. Only a flesh wound," Frank responded eagerly. "Then take this light," the colonel ordered, "and follow him at a distance of a hundred yards. If anything should happen to your friend, you follow the directions you have just heard." "Yes, sir," the lads responded in unison, and, with a hasty salute, were off.