No sound reached them. It was a moment of agonizing tension. Then, nearer than before, they heard the picks again. Suddenly the sound ceased. The invaders had completed their work. There was no time to lose. At a sign from the officer, who brushed a handkerchief across his face and drew a laboured breadth, a grim-faced sergeant began to crawl back swiftly to the distant opening of the tunnel for the dynamite. Another and more torturing pause ensued. Which mine would be exploded first? It was an affair of minutes, then of seconds. Their mine was not yet ready. But duty held them to their ground. Though hell should burst upon them on the instant, the flaming portals must be faced. Out in the open, those who watched and waited suddenly heard a thunderous detonation. A huge mass of earth and chalk rose high in the air, and clouds of whitish smoke spread skyward in the full glare of the searchlights. Three engineers, half doubled up, now came rushing from the tunnel to the outlet, bursting among a little group of officers, who staggered back with horror in their faces. "Done for ... countermined!" One of the sappers gasped out the fateful words, then sank exhausted on the ground. "My God!" exclaimed Helmore, the officer in charge of the relief party, falling back a pace. Then, promptly recovering his self-control, he cried: "Forward to the rescue. Some of our men may be alive!" He himself dashed into the tunnel, followed by half a dozen men. At a little distance, the narrow avenue was blocked. The miners were entombed! but an indirect opening had been made by the concussion, which gave the rescuing party access to another tunnel. Following this, and finding it intact, Helmore, in advance of the party, raised his lanthorn and saw in the distance an exposed angle of a massive concrete wall. He understood at once that the exploded mine, working in a lateral direction as well as upward, had exposed the caponiere, or covered lodgment under the counter-scarp, which Wardlaw had sunk in that position designedly for the protection of the Fort. Therefore, the holders of the Fort, in a measure, were hoist with their own petard. Their mine had exploded first, but at the same time it had exposed a point against which a subterranean attack now might be directed.