"Still," Jupiter went on thoughtfully, "a Nevada licence plate is most interesting. As far as we know, no one around the ranch has anything but a California plate."
"You mean there"s someone around here we don"t know?" Pete said.
"Sure there is," Bob told him. "That man with the eye patch."
"It looks that way," Jupiter agreed, "but now we must get to work. I"ll look through that book on Moaning Valley while you two go down and check the scuba equipment. Wrap the tanks in something that will disguise them, and then put them on the bikes with the candles, the sombreros and the bundle I brought."
"The plan!" Bob and Pete said together. "What is it?"
"I"ll tell you on the way," Jupiter said, and looked at his prized chronometer. "We have to hurry now if we"re going to reach Moaning Valley before sundown. Tonight we may solve the mystery of Moaning Valley!"
Half an hour later the First Investigator appeared in the barn, waving the book at Bob and Pete.
"I think I"ve found part of the answer," Jupiter announced. "It says here that about fifty years ago they sealed up many of the old mine shafts in Devil Mountain. They had never found any gold or anything else, so they closed the tunnels. Fifty years ago was when the original moaning sound stopped!"
"You mean one of them has been opened up again?" asked Bob. "And the wind blowing through it causes the moaning sound?"
"Yes, I think so," Jupiter agreed. "The question is how and why? ... Are you fellows ready?"
"Ready, Jupe," Pete said.
"All right, then put on the sombreros before we ride out of the barn," Jupiter instructed.
The boys donned the wide-brimmed straw hats, balanced the heavy tanks disguised in burlap sacks, and mounted their bikes. The bikes proved somewhat hard to handle with the weight on them, and it was clear that they would have to pedal with care.
"Ohhh," Bob cried, wincing with pain.
"Is it your ankle, Bob?" asked Pete.
"It"s all the weight on the bike," Jupiter decided.
Bob nodded unhappily. "I don"t think I can make it, Jupe. I guess I"ll have to stay behind."
Jupiter had his thoughtful look. "No, I don"t think you will have to stay behind, Bob.
Perhaps we can turn this misfortune into an advantage. It will make our deception more convincing."
"What deception?" Pete asked, bewildered.
"The cla.s.sic military tactic of the camp-fires and logs that look like cannon," Jupiter explained obscurely. "Bob, unload your scuba equipment. Without the weight I think you can operate the bike."
Bob tried again and found that without the extra weight he could indeed pedal satisfactorily. The boys rode out of the barn towards the gate. As they pa.s.sed the house Mrs. Dalton waved from the porch.
"Have a good time, boys, and don"t stay out too late!" she called. "And be careful!"
Once out of sight of the ranch, the boys pedalled faster towards Moaning Valley. When they reached the place where the road ended at the iron gate, they dismounted and carried their bundles and their bikes into the thick bushes.
"Now," Jupiter said, "here is my plan. We"re going to get inside the cave without being seen."
Pete nodded. "I get it. We"ll take the moaning by surprise."
"Right," said Jupe. "Of course, if my theory is correct we"re being watched closely right now!"
"Gosh," Bob said, "then how do we do it?"
"We go under water," Jupiter told them, "using the scuba equipment. I checked on the tide and it"s higher this evening. I estimate that most of the tunnel from the beach will be under water."
"But, Jupe," Bob objected, "how will we get into the water without being seen if we"re being watched now?"
Jupiter beamed triumphantly. "We will use the decoy tactic. The way armies used to light camp-fires at night, and then slip away in the dark."
"But-" Pete began.
"You see," Jupiter went on, "I also noticed last night that while the trail to the right is in clear view from the top of Devil Mountain, the trail to the left is hidden. Come on. Walk casually and in the open."
The three boys climbed over the iron gate and continued down the cliff path to the left.
When they were just out of sight from the top of Devil Mountain, Jupiter said, "Stop here."
The boys put down the scuba tanks, and watched as Jupiter opened the secret package.
"That"s just old clothes!" exclaimed Pete.
"The same as those we"re wearing!" Bob added.
"Exactly," said Jupiter. "Stuff them with brush, and tie off the arms and legs with this cord."
Bob and Pete did as Jupe said and in a few moments they had two dummies that looked remarkably like Pete and Jupiter.
"And the sombreros will hide our faces!" Pete said.
"Precisely," agreed Jupiter. "In addition they can be easily seen from the top of the mountain. Whoever is up there will be convinced that the dummies are us, especially since Bob will stay here with them and move from time to time!"
Quickly the boys set up the dummies above the trail. Bob sat beside the dummies, pretending to talk to them. From a distance it would look exactly as if The Three Investigators were sitting at the cliff edge observing the view.
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 tonight," 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 compa.s.s 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.
Chapter 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 compa.s.s.
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 sh.o.r.e. Pete nodded. It was time to start in for El Diablo"s Cave.
Jupiter continued to lead the way. Closer to sh.o.r.e 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 b.u.mped 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 pa.s.sage.
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 pa.s.sage 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 pa.s.sages. 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 pa.s.sage.
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.