“I suppose you’re right,” Jupiter said reluctantly. “Bring El Diablo’s pistol and we’ll try to find the tunnel that leads out of here.”
Pete lit his candle, and the boys started for the next tunnel to test for a current of air.
Suddenly there was a faint ripple in the water of the pool that had been so dark and silent. This was followed by splashing and loud breathing. The boys stood motionless, their flashlights trained on the sound.
A black and shiny shape broke the surface of the murky pool. Water dripped from its shining skin, reflecting in the beams of the boys’ flashlights, as the creature raised itself out of the water.
Jupiter and Pete stared in horror as the shiny black creature began to climb out of the pool.
“What are you boys doing here?” the creature demanded.
Suddenly, at the same time, both boys realized what they were looking at. It was a man wearing a black rubber wet-suit, swim fins, a double air-tank painted black, and a black rubber mask that completely covered his face.
“Oh, boy!” Pete exploded in relief.
Jupiter, recovering immediately, drew himself up to his full height, his round face suddenly looking much older. It was an old trick he used when dealing with adults, and it usually worked as well as his other surprises.
“What, sir, are you doing here?” he asked in his deepest voice. “We are here by permission of the owners of this ranch. You, apparently, have come in by some secret entrance that leads from the sea. You are trespassing.”
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.”