“You have ‘Flat Rock’ marked here over the cave,” he said. “Is that the rock you were sitting on when Wally dropped his knife?”
“Yes, that’s the one,” Jim answered. “It has a cleft in it through which the knife went down—just wide enough to admit the knife. It’s really a kind of lid over the rocks that form the first cave.”
“And you said there were loose boulders lying on it?”
“Yes; big fragments of rock. I should think that a big chunk of the cliff must have fallen on it once, probably splitting it and making the crack, and breaking itself as well. A lot of it went down: the biggest piece buried itself partly in the sand.”
“That’s the boulder that almost hides the entrance, then?”
“It’s about three feet from the entrance and a good deal wider than it,” he said. “There are so many similar rocks lying about that it would be quite easy to miss the cave altogether.”
“Then I take it that the top of the flat rock is above high-water mark?”
“Oh, yes,” Jim answered. “High-water mark is about a foot over the top of the entrance, and the rock is quite four feet higher than that. Otherwise I don’t fancy the waves would have left those big pieces of loose rock lying on it.”
“That’s what I wanted to know. Now listen. Suppose the Germans land, and most of them disappear into the caves, to fish for petrol. What is to hinder two active people, armed with levers, from sending down from the top of the rock enough boulders to block the entrance?”
Jim started, his pipe falling from his hand.
“By—Jove!” he uttered. “What a ripping idea!”
“Why, we could do it as easily as possible,” Wally said, excitedly. “The rocks are quite close to the edge: one of them is so loose that we were rocking it this afternoon. We’ve pretty hefty muscles—we could send half a dozen over in no time with a couple of iron bars. Glory, O’Neill, you _have_ a head!”
“Yes,” said Jim, his eyes dancing—“and they could hardly miss the entrance, because the big boulder in front would prevent their rolling out too far. What chumps we were, not to think of it, Wal!”
“Then you’d have the Germans like rats in a trap—and with no shooting at all!” Norah cried, delightedly.
“Something like that: with luck,” said O’Neill. “Of course, they would have a guard posted outside, and another at the boat. But the main crowd would be inside, I should think.”