"Deep water always is," replied Gerald, as he prepared to follow his companion's example. "Are you going to get the dinghy aboard?" he asked, after the ablutionary exercises had been completed. "She's a bit of a drag astern, I fancy." "No; let her stop. I'm going to turn in now. If it comes on to blow--I don't think it will--give me a shout, and we'll soon whip the dinghy aboard and lash her down securely. In any case turn me out at eight bells." Gerald thereupon took charge of the helm. The _Playmate_ had already reeled off more than thirty miles of her cross-Channel passage. But though the atmosphere astern was perfectly clear, ahead the horizon was obscured by a haze that blended sea and sky together in an indistinct blurr. The wind, too, was slowly yet gradually dying away, and the yacht was doing little more than two knots. With the falling of the wind the haze increased in density, so that, two hours after Gerald had taken the helm, the _Playmate_ was fairly in the thick of a dreaded sea-fog. "Jack, old man, have you a fog-horn aboard?" Stockton was wide-awake in an instant. "By George! This is thick," he exclaimed, for already the yacht's bowsprit end was lost to view in the white, curling vapour. "No, I've no fog-horn; I always use a rowlock. Here's one. We'll lash it up to the sliding-hatch." This done, he struck the suspended rowlock a couple of sharp taps with a mallet. "There's enough noise to warn any vessel within a cable's length of us," he continued. Gerald grunted. He knew the ways of the sea. A tramp steamer, forging through the fog at a steady eight knots--as they frequently do--would not pay much heed to anything less than a siren. "All right," he assented; "I'll see to that. You may as well turn in again." "I've had enough sleep to last me for a time," replied Jack. "I'll keep watch with you. Here, put this on, or you'll get soaked to the skin," he added, producing an oilskin from one of the lockers, and proceeding to don a second one himself. "What's that?" asked Gerald, after a prolonged interval, as a dull, pulsating sound, quite unlike the noise of a steamer's engines, was borne faintly to their ears. "Hanged if I know! Here, old chap, get a sweep out, and keep way on her. I'll sound the fog-bell." Tregarthen did as he was asked, for the yacht was now practically becalmed, while Stockton made a vigorous onslaught upon the improvised fog-bell with his mallet. Nearer and nearer came the mysterious vibrating sound; then, with appalling suddenness, a shrill, long-drawn blast from a siren sounded as if from overhead. "By Jove! We'll be run down!" exclaimed Jack, calmly, though he fully realised the danger. The next instant a hoarse voice shouted: "Ahoy there! Starboard your helm!"