The skin-diver reached up and removed his rubber face mask. He was a handsome, blond man and he was grinning at Jupiter. Unhooking his air-tanks, he laid them on the floor.
“Well, son, you sound almost as important as the admiral,” he said. “I wasn’t questioning your right to be here. I was just wondering what two boys were doing in El Diablo’s Cave this late at night.”
“The admiral?” Jupiter looked puzzled for a moment. “Of course! You’re a frogman, aren’t you? A Navy frogman on training manoeuvres with those ships out near the islands.”
The frogman looked serious. “Yes, that’s exactly what I am. We’re on a highly secret training mission here. I’ll have to swear you boys to complete secrecy. Have you seen anything in the water you thought was unusual?”
“No,” Pete said.
“Nothing, sir,” Jupiter assured him. Then, remembering suddenly, he snapped his fingers. “Except that shape!”
“Shape?” the frogman repeated.
Now Pete remembered too. “That long, black thing that passed us out in the ocean.”
“It was a submarine, Pete!” Jupiter exclaimed eagerly. “A midget submarine. That was why it was so rigid, and why it moved so steadily. But why didn’t we hear its engines? Sound carries very far under water.”
The frogman’s face darkened. “This could be very serious, boys. That submarine you saw is top secret — especially the silence of its engines. I’m afraid I’ll have to hold you.”
“Hold us?” Pete echoed.
“A submarine that moves so silently that it can’t be detected by sonar is very important, Pete,” Jupiter said solemnly. “However, I believe we can prove that there is no need to hold us, Mr…. ”
“Commander Crane,” the frogman said. “Commander Paul Crane. And I’m sorry, but I am going to have to hold you — at least until the admiral can have you investigated.”
Jupiter nodded understandingly and tried to look dignified, which wasn’t easy when he was wearing only bathing trunks and a diving belt.
“We’re Jupiter Jones and Pete Crenshaw,” Jupiter said, and reached into one of the waterproof containers which hung from his diving belt. “I believe these credentials will attest to our complete reliability.”
Jupiter handed the commander the boys’ business card and the special deputy cards given to them by Chief Reynolds of the Rocky Beach police. Commander Crane studied the cards.
“We happen to be involved in an important case right now,” Jupiter told him. “That is why we are in this cave. I’m sure your admiral would want you to co-operate with us. Commander.”
Commander Crane looked at Jupiter and hesitated. The First Investigator could be very impressive when he was being serious and professional.
“Well now,” the frogman said, “these cards do make you boys seem legitimate.”
“Why don’t you communicate with your ship,” Jupiter suggested, “and have them check at once with Chief Reynolds in Rocky Beach. I’m sure he will vouch for us.”
“Gosh, Jupe,” Pete exclaimed, “how can the commander talk to his ship from in here?”
“A good frogman is always in contact with his ship,” Jupiter informed Pete. “I assume that the commander has some form of long-range radio.”
Commander Crane smiled. “You’re a very smart boy, I see. All right, you boys just sit down and stay put.”
Jupiter and Pete did as they were told, and Commander Crane vanished into the darkness. Minutes passed. The boys could barely see the frogman crouched in the dark of the cavern. He was bending over a tiny instrument of a type the boys had never seen before. Jupiter watched with curiosity, but he could not make out what was happening.
At last the commander straightened up again, replaced his instrument in a hidden pocket, and strode back to the boys. He was smiling.
“Security says you boys check out,” he said. “I won’t have to hold you.”
“Gosh, you move fast,” Pete said.
“We move fast when we have to,” replied Commander Crane. “The admiral has pretty high priorities.”
“Now that we’ve been approved, Commander,” Jupiter said seriously, “may we ask you some questions?”
“Me?” The frogman shook his head, smiling. “I’m afraid that won’t be possible, boys. My work is also highly secret.”
“It’s not about your work exactly, sir,” Jupiter assured him. “I want to know about this cave. First, was it you Pete saw last night up near the front of the cave?”
Commander Crane nodded. “It was probably one of my men. He reported that he had been spotted briefly.”
“That makes me feel better,” Pete said. “At least it explains another mystery of the cave.”
“Second,” Jupiter went on, “did you or your men make any changes inside, the cave? I mean, did you change the layout of the cave, the various tunnels and openings, or anything like that?”
“No,” the commander said, “I can tell you that much.”
“Third, sir,” Jupiter enumerated, “is anything you are doing causing the cave to moan as it does?”
“Absolutely not. We wondered about that moaning ourselves. Of course, we’ve only been in the cave a few times. We haven’t been in this area long. We assumed the cave always moaned like that.”
“And your work requires you to remain completely unseen if possible?” Jupiter pressed on.
“Absolutely.” The commander smiled. “As a matter of fact, I’m sure we haven’t been seen by anyone but you boys. Most of our work has been done on the ocean side of the cave, and here near this pool.”
“Have you seen anyone else in the cave?” Jupiter asked.
Commander Crane shook his head. “No, it is essential to our training mission that we remain unseen. Of course, there is no enemy here, but we try to avoid any contact with anyone.”
“Of course,” Jupiter said with a sound of disappointment.
“I’m sorry, boys,” Commander Crane said, “I’d liked to have helped you. Can you find your way out of this cavern?”
“We’ve been trying to find our way,” Pete blurted out. “That’s what we were doing when we saw you.”
“Well, I think I can set you on the right track,” the commander said. “Remember, you must not talk about anything you have seen here involving our operation.”
“Yes, sir!” Pete agreed.
“Of course, Commander,” echoed Jupiter.
“All right, then, follow me.” The frogman led the boys to one of the tunnel openings, then through several caverns and side passages until they emerged into the large cavern where Pete had first seen the mysterious black and shiny shape.
“All right, boys,” Commander Crane said. “I expect you can make it from here. I must get back to my work.”
“Thank you, sir,” said Jupiter.
The frogman smiled at them. “And good luck with your work.”
He vanished back into the small opening, and Pete started for the tunnel that he remembered led out to Moaning Valley.
Jupiter made no move to follow. He was staring into empty space with that faraway look Pete knew only too well.
“Oh no!” Pete groaned. “Don’t tell me, Jupe.”
“I’m more certain that ever that we have to solve the mystery to-night, Pete,” Jupiter said. “The man disguised as El Diablo knew we would find our way out eventually. That means he didn’t care how much we knew as long as we couldn’t get in his way until some hours from now.”
“I don’t want to get in his way at all,” Pete observed, “but something tells me I’m going to.”
“This is our real opportunity, Pete,” Jupiter insisted. “Whoever is trying to scare people off thinks we’re still out of the way! We’ll never have a better chance to locate that digging and find out what makes the cave moan.”