“You’re right, kid,” said Stone.  “I’m no more of a coward than the next fellow.  But if Morales and Von Arnheim by any chance gained the upper hand and got their clutches on me, I’d hear the birdies sing.”

Frank had been thinking rapidly.

“Look here,” he said, “isn’t there some way we can sneak up there to find out if matters are all right or not?  Suppose Tom has been overcome.  We wouldn’t stand much chance approaching the cave by the regular entrance.”  He paused and again stared upward.  “We’ve been gone a considerable time,” he said nervously.  “You’d think if he were all right, Tom would have called to find out what is delaying us.”

“Tell you what,” said Stone, “I’ve got a little private path to the top of the cave where the antenna is located.  It isn’t much more than a goat track.  But we’ll have to be goats.  Never been up it in the dark, but I think I can make it.  Are you game to follow me?”

“Certainly,” said Frank, “if it will be of any advantage for us to do so.”

“Well, there’s a fissure through the rock down into the cave.  That’s where the Germans that put in the radio plant made their hook-up.  We can listen there, and maybe hear something to guide us.”

“Oh, I remember that,” said Frank, and added excitedly:  “Maybe I could crawl down into the cave.”

“You might be able to, at that,” said Stone.  “You’re pretty slight.  But it would be a ticklish proposition without any rope from above.  Well, if you’re on, let’s go.”

Turning he struck off across the valley, approaching the hill some distance from the path leading to the cave.  Frank followed closely at his heels.  Soon they began mounting upward.  The climb in the darkness became more and more difficult, made more so by the care they exercised to prevent dislodging stones.  They feared the clatter of these descending to the bottom would betray them.

Once Stone, who was in the lead, slipped and slid backward, clutching frantically to stay his fall.  Fortunately, Frank was well braced at the moment and was able to stop him.  After a rest to regain their breath and calm their shaking nerves, they resumed the climb.

At length Frank’s feet were on level ground and ahead he saw the outlines of two latticed towers of familiar construction, and between them overheard the strands of the antenna.  The Germans, Stone earlier had explained, had built the towers in such fashion that the crest of the hill hid them from the plain on one side while they were so far back from the edge of the flat plateau crowning the hill as to be also hidden from view from the valley.

Whispering an injunction to Frank to follow close at his heels, Stone crawled on hands and knees to the fissure in the rocks down which led the wires of the hook-up.  It was not a straight descent into the cave, and no light came from it.  But the two knelt in the darkness and put their heads close to the black opening to listen.