Hidden below the cliff, Jupiter and Pete slipped down the trail to the small beach at the bottom. There they struggled into their air-tanks.
“The surf is light to-night,” Jupiter said. “We should have no trouble swimming from here to the cave entrance.”
Pete nodded. “Underwater it shouldn’t take more than five minutes to swim that far with our nippers.”
“Right,” Jupiter agreed. “I have my compass and if necessary we can surface briefly. Our decoys should keep anyone from bothering to watch the ocean.”
The boys fixed their breathing tubes in their mouths, walked backwards into the water, and slid beneath the waves.
11
Shadow Under the Sea
Pete followed Jupiter’s waving fins through the bright, translucent water. Both boys were experienced scuba divers and swam only with their feet, with no wasted motion. Pete maintained a wary watch on the dark shadows of the rocks, while Jupiter concentrated on following the direction with his wrist compass.
Fish darted around them, and one large halibut, which had, been invisible against the bottom, startled Pete by separating itself from the rocks and swimming majestically away.
After a couple of minutes, Jupiter stopped and turned to face Pete. He pointed to his diving chronometer and then towards the shore. Pete nodded. It was time to start in for El Diablo’s Cave.
Jupiter continued to lead the way. Closer to shore the water was murky, and there were more rocks, so Pete swam closer to the flapping fins in front of him. In fact, he swam so close that he bumped hard into Jupiter’s back when the First Investigator suddenly stopped.
Pete grunted, a little annoyed. His annoyance abruptly vanished as he saw that Jupiter was frantically pointing to the left. Pete looked.
A dark shape moved slowly through the water no more than thirty feet from them. It was large and long, like a big, black, hazy cigar — the shape of a shark or even a killer whale!
Pete’s heart thudded. But the boys had been carefully instructed about what to do if they ran into a shark. They reacted to their training instantly. Moving as little as possible, since movement would attract a shark, they sank to the bottom. They drew their diving knives as a precaution, and began to edge their way slowly towards the safety of the rocks.
Pete watched the shape intently. He decided that it moved too steadily, too rigidly in a straight line, and was too long for a shark. At the same time, it seemed too small and slow for a killer whale.
Jupiter touched him on the shoulder and made the sign for a shark. Pete shook his head and both boys watched the strange shape slowly fade away out to sea. Then they swam in until the surge of the surf told them they were close to the cliff of Devil Mountain. They surfaced cautiously and found themselves only a few feet from the cave mouth.
“What was it?” Jupiter asked as soon as he removed his mouthpiece.
“I don’t know,” Pete replied nervously. “I’m pretty sure it wasn’t a shark or whale or any kind of fish. Maybe we should go back, Jupe, and get the sheriff.”
“If a whole posse came here they wouldn’t find anything,” Jupiter pointed out. “Whatever that shape was, it was going away, right? I’m sure that there is some simple explanation for it and, anyway, it’s gone now.”
“Well… ” Pete hesitated.
“Now that we’re this far, it would be foolish to turn back without investigating the moaning,” Jupiter said decisively. He always hated to give up once he was on a trail.
“Come on, Pete. I’m going into the cave. You hold the rope until I’m inside.”
Jupiter vanished under the water. The sun was almost down now, and in the darkening twilight Pete waited with the rope in his hands. When he felt a double tug, he fixed his mouthpiece in place and swam into the narrow passage.
There was little surf and no current and Pete’s waterproof flashlight, which was fastened to his gear, gave plenty of illumination. The water in the tunnel became quickly shallow as the floor angled upward, and soon Pete was standing in the large cavern beside his friend. The first thing he noticed as he took off his swim fins was the sound.
“Aaaaaaahhhhhhhhhhhh — oooooooooooooooo — oooooo — oo!”
The cave was moaning!
Jupiter was grinning like a contented cat. They were inside and the cave was actually moaning.
“Gosh, Jupe,” Pete whispered, “you were right! No one saw us come inside, so the cave’s moaning.”
“It certainly seems that way, doesn’t it?” Jupiter said somewhat smugly. “And it’s just about twilight — the exact time of our first visit here last night. Come on!”
Quickly they took off their diving gear. Jupiter struck a match from his waterproof box and lighted two of the candles.
“We’ll carry the candles to the mouths of all the tunnels that lead out of this cavern,” Jupiter explained. “If the candle flickers it means there is a current of air moving through the tunnel. If the flame doesn’t move, that means the passage is probably blocked. It will save us a great deal of time and wasted searching.”
Pete nodded. “Smart idea!”
Quickly they began to test the passages. At one, the candle flickered slightly. But Jupe was not satisfied. Pete went into the next tunnel. Suddenly the flame of his candle was drawn strongly into the dark opening.
“Here, Jupe!” Pete called excitedly.
“Shhhhhh!” whispered Jupiter. “We don’t know how close we may be to somebody.”
Both boys held their breath and listened. For a long half-minute all was silent and Pete was furious at himself for shouting. Then the moan came again, faint but clear.
“Aaaaaahhhhhh — ooooooooooo — ooooo — oo!”
It seemed to come straight out of the tunnel that was attracting the candle flame. Jupiter took out his chalk and marked a small white question mark at the entrance to the passage. Then the two boys lit their flashlights and plunged into the tunnel.
Back at the cliff top, Bob sat with the dummies, watching the flaming orange sun set in the west. Slowly, a purple and red twilight settled over the ocean. Bob stretched his legs cautiously.
He had been sitting there talking to himself for over a half-hour, he guessed, and during all that time he had had the feeling that eyes were watching him. He knew that it was probably just his imagination, but it was a weird feeling anyway.
To occupy his mind, Bob began to read the book about Moaning Valley. He read the part that told of the mine shafts being sealed, and then he read further. Suddenly he sat up very straight.
“Gosh!” he exclaimed in a whisper.
He had come to a passage about Old Ben Jackson and his partner, Waldo Turner. The book said that Old Ben and his partner lived on a ridge right next to Devil Mountain and that they had dug one of the mine shafts into the mountain. Their shaft had been sealed up with the others, but Old Ben and Waldo had refused to leave. They insisted they would keep prospecting for gold — and diamonds!
Bob frowned. He was sure that Jupiter, in his eagerness to get started on his plan, had not read this far in the book. If Jupe had read that Old Ben thought there were diamonds around Devil Mountain, he would have mentioned it.
In the growing darkness Bob was suddenly worried. Jupiter thought that the moaning might be caused by the reopening of one of the old shafts. Old Ben and his partner had actually dug such a shaft themselves, and they probably knew El Diablo’s Cave better than anyone else, after living right next to it for so many years. It would be simple for them to reopen a shaft.
Then Bob thought about something else. He remembered how Old Ben had surprised them the previous night. They had been inside an inner cavern, yet Old Ben had claimed he was passing by outside the cave and heard them! Suddenly, Bob realized that this would have been practically impossible. The distance was too great. Old Ben must have been inside the cave when he heard them, which meant that he had lied to them.