"Be not frightened, lads, but pull out as fast as you can for the ship; there are sharks coming after you!" Their hearts leapt in their breasts at this startling news, and, looking hurriedly round, they perceived, to their horror, that several black triangular dorsal fins were cleaving the water in their wake, and closing rapidly in upon them. Fortunately the water in the direction in which they were swimming was as yet clear, to all appearance. "Cannot you send a boat, sir? We are nearly exhausted with the swim," hailed Roger, who was slightly in advance of Harry. "Nay, that I cannot, lad, for all the boats are still on shore. You must swim, and for your lives' sake swim hard," answered Cavendish from the deck of the ship. He was leaning anxiously over the bulwarks, and the rail was lined with the faces of the few seamen who were left on board, while two of them had gone down the accommodation ladder and were waiting at the foot, ready to haul the lads in as soon as they were near enough. The men on board now quickly seized whatever missiles they could lay their hands on, and stood ready to bombard the sharks, in the hope of driving them off, if they did not seize the lads before they got within range. As for Harry and Roger, they struck out with the energy of terror; but each felt that he was tiring with every stroke, while the knowledge that at any moment they might feel themselves in the jaws of one of those sea-tigers seemed to paralyse their limbs. Their flesh crept with the horror of the thought. Harry, especially, was showing manifest symptoms of increasing distress; while Roger, resisting the impulse to swim on and reach safety, kept valiantly at his side, encouraging him. "Go on, Roger," at length gasped Harry; "I am done, and cannot reach the ship. Swim you on and get on board; I will follow if I can." "Nay, Harry, lad," answered Roger, "either we both get on board, or--or not; we did not make our compact to break it at the first sign of danger. Do your utmost, and we shall yet get on board all right." Even in his extremity Harry could not avoid noticing that Roger hesitated when he came to "or--or not;" the brave lad could not bring himself to utter the alternative in words. Before leaving the shore the boys had stripped down to their pantaloons and vests, which they had retained as a makeshift bathing-costume. Now, as luck would have it, Roger invariably wore a belt round his waist, to which was attached a very fine Venetian dagger, slender of blade, sharp as a razor, and very strong. This had been given him by his father as a parting keepsake, and he looked upon it almost as a kind of talisman; he therefore never allowed it to leave his person. Merely by force of habit he had buckled this belt and dagger about him before starting for the swim, and now, in the moment of his deadly danger, he suddenly recollected that he had it on him, and an idea came to him like an inspiration.