The other approached warily, but there was a suggestion of triumph in his movements. He began circling round his prostrate opponent, seeking a favourable opportunity of closing. He hesitated, possibly because he feared a ruse on the part of the Englishman, who, with knife uplifted, kept turning so that he was always face to face with his assailant. Obviously these wearing-out tactics were telling upon Swaine. The longer the other delayed, the worse became his state owing to the poor quality of his air-supply. At length the unknown diver raised his arm to deal a stroke. He did it dramatically, pausing with the blade held high above his head. With senses dulled, Swaine steeled himself to meet the deadly stroke, but the stroke never came. A rush, a swirl of water, and a blurred vision of the other diver sinking slowly on his face told Swaine that deliverance had come from a totally unexpected quarter. A huge shark, attracted by the glitter of the knife, had bitten off the fellow's hand just above the wrist, at the same time tearing the india-rubber cuff of his diving-dress and allowing a considerable amount of air to escape. The shark, finding its palate unpleasantly tickled by the sharp steel, and not laying claim to be a sword-swallower, decided that one mouthful was enough and made off for pastures new, leaving the interrupted principals of the submarine duel to settle matters as best they could. CHAPTER XXVIII The Explosion The instinct of self-preservation, coupled with the fact that he yet had a faint chance of escape, rallied the semi-torpid Swaine sufficiently to enable him to take action. He dropped the knife and groped for the release-valve of the compressed-air reservoir. Half a turn, and he felt the buoyant air rushing into the double folds of his diving-suit. Even as he realized that he was parting company with the bottom of the lagoon he found himself looking at his late antagonist, who was writhing in agony, with a ruddy stream mixed with air-bubbles rising from the clean-cut stump of his severed arm. Not knowing why he did so, whether it was the irresponsible act of a light-headed man, the sudden impulse of an overstrung brain, or generous pity for a beaten foe, Swaine gripped the fellow by the arm, at the same time turning the release-valve of his buoyancy-flask full on. Up he shot to the full extent of arm's length and no farther. The lifting powers of the inflated diving-dress were sufficient only for one. Weighed down by his former antagonist, Swaine saw no chance of bringing the latter to the surface, until an inspiration seized him. Having once set his hand to the plough, he was loth to turn back until his task was completed.