Wally assented, more or less reluctantly; and Jim took off his boots and stockings and rolled his trouser-legs high. Then, he stepped carefully into the black pool. “By Jove, it’s cold!” he said. “What’s the bottom like?” “Fairly smooth.” He moved on, becoming less cautious. Then he uttered an exclamation. “What’s up?” came from Wally. “I’ve stubbed my silly toe against something—my own fault.” Jim answered. “Why, it’s another tin!” He stooped, feeling in the water. Presently he let go of the stick, and plunged both hands in: and in a moment turned, carrying something that was evidently heavy. He put it on the rock at the edge of the pool, and stepped out of the water. Wally flashed the light on the treasure-trove, and then whistled softly. “Petrol!” Jim nodded. “The pool is full of it, I believe: I felt lots of other tins.” He turned the big square can over and over, finding no mark upon it. “H’m. Now I’m going to put it back.” “Why are you in such a hurry?” “Because I don’t know whom we have to deal with,” Jim said. He waded in again and replaced the heavy tin, returning quickly, and picking up his boots and stockings. “Slip out and reconnoitre, carefully,” he said. “Take care that you aren’t seen. Find out if anyone is in sight.” Wally returned in a few minutes. “Not a soul,” he reported. “And there’s not a footmark visible on the sand, except our own.” “That’s good, anyhow,” Jim said. “We’ll get out of this.” He led the way out, not speaking until they were clear of the rocks near the cave. Then he sat down, and for the first time the two boys looked at each other. Their faces were grave. “It’s submarines, of course?” Wally asked. “Germans?” “Couldn’t be anything else. And what a depôt! Look at this inlet—shut in by the headlands, with a perfect sandy bottom: a submarine could come in here and lie in complete safety, and no one would ever dream of looking for her. The cave is not five minutes from the water’s edge, even at low tide—of course, no one could get in to it at all unless the tide were right out: when it is in there’s a foot of water over the entrance.” “Yes—and at low tide the sand is as hard as iron,” Wally said, excitedly. “They could fill their collapsible boat with petrol tins in ten minutes with two or three men to fish them out of the water and a few more to carry them down. Oh, Jimmy, we’ve got to bag them!” “Rather!” Jim answered. “The question is, how?” He thought deeply. “We must be awfully careful,” he said, at last. “It’s much too big and important for us to mess up by trying to keep it to ourselves. But there isn’t a policeman in the district, and if there were, he might mess it up as badly as ourselves. We’ve got to get a patrol-boat round to the inlet somehow; you know they’re all round the coast, and it wouldn’t take long to bring one here. But one doesn’t know whom to trust. The Germans may be getting help from on shore, for all we can tell.”