Rollo, too, offered no objections to being relieved of his duty. The vibration of the wheel, almost unnoticeable under ordinary circumstances, was causing his wrist intense pain. He handed Thelma the charge of the helm, told her what course to take, and sat down, admiring, in spite of his physical anguish, the alert, self-possessed girl as she toyed with the spokes of the wheel with the ease of a practised helmsman. "We're up to that vessel, Rollo," she reported, after an hour had passed. Owing to her superior speed the motor-boat had rapidly gained upon the lumbering ten-knot tramp which was now a couple of cables distant on the port hand. Her companion bestirred himself and went into the cabin. "I wouldn't wake Kenneth," he said as he reappeared. "Yvonne tells me he's quite done up." "I wonder you're not, too." "I'll make up for it when we get ashore, never fear," declared Rollo. "But the point is, we've got to steer a course. Here's the compass, but it's almost like Greek to me. I suppose if we keep due west we'll do something? There are such things as variation and deviation, but, although I did have a chance, I never troubled to understand them. I wish I had, now." Providentially, for it was now close on high water, the little craft crossed the dangerous sand-banks that encumber the Scheldt entrance without any of her crew realizing the risk they were running. Once they encountered "overfalls" of rather broken water on the tail of a bank; but, with nothing worse than a couple of waves breaking inboard, the motor-boat gained the comparatively smooth water beyond. Grey dawn was now breaking. All around was an unbroken expanse of sea and sky. Not a vessel or a buoy of any description was in sight. For the first time Rollo was able to form some idea of the vastness of the North Sea. Bestirring himself, he examined the petrol-gauge and the quantity of oil in the automatic lubricator reservoirs. The consumption of both had not been excessive, and the motor was running like clockwork. "It's getting very misty," said Thelma. "By Jove, it is!" assented her companion. "I hope it won't come on any thicker. Are you cold? Let me take the wheel again." The girl shook her head. "I'm quite all right," she declared. "I am enjoying it. How much farther is it, do you think?" It was Rollo's turn to shake his head. He did not know, and he was too candid to pretend that he did. "We ought to be meeting shipping in and out of the Thames estuary shortly," he said. "I suppose our merchant vessels sail as freely as they did before the war? Hello! There's something coming up astern." He pointed to a faint blurr of smoke about three miles away and dead in the wake of the motor-boat. "Something fairly fast to be able to overtake us," remarked Thelma. "Is there a telescope on board?" "I'll see," answered Rollo.