“And I hear noises,” Pete added.
“Yes,” Jupiter said firmly. “But that is your imagination. In eerie surroundings like these, the simplest sound seems frightening. Now are we all ready? Bob, check the flashlights again.”
Bob tested the flashlights and Pete looped the rope over his shoulder. Each boy took his piece of chalk in his hand.
“Caves can be dangerous unless you take the proper precautions,” Jupiter explained. “The main dangers are falling into chasms and becoming lost. We have the rope in case any of us fall, and by marking our trail with chalk no one will become lost. We will stay together at all times.”
“Shall we mark our trail with question marks?”
“Right,” Jupiter said. “And we will also use arrows to indicate the direction we have taken.” The question marks in chalk were one of his most inspired inventions. The boys used them to leave a trail. The marks instantly made it clear that one of the investigators had been in a place. Since Jupiter’s chalk was white, Pete’s blue, and Bob’s green, it was even possible to tell exactly which one had made the marks.
“Well,” Pete said. “Are we ready?”
“I believe we are,” Jupiter said, satisfied at last.
The boys took a deep breath, and then began to walk down the slope of the ridge into the valley.
Once more the moan wailed out in the night “Aaaaaahhhhhhh — ooooooooooo — oooooo — oo!”
A swift current of cold air came to meet them as they neared the dark opening of the cave. Jupiter, in the lead, had already switched on his flashlight when suddenly he heard a rumbling sound.
“What’s that?” Bob cried.
The sound grew louder. Because of the strange echoing effect in the bowl-shaped valley, it seemed to come from all around them.
“Look up there!” Pete shouted, pointing.
A giant boulder was tumbling down the steep face of Devil Mountain in a shower of smaller stones.
“Jump!” Pete cried.
Bob hurled himself sideways out of the path of the hurtling boulder.
But Jupiter stood frozen, staring at the great rock as it fell straight towards him.
Pete threw himself at Jupiter, knocking the First Investigator away from the mouth of the cave. The boulder struck the ground with shattering force directly where Jupiter had been standing.
Bob scrambled to his feet. “Are you all right?” he asked anxiously.
Pete stood up. “I think so. Are you, Jupe?”
Jupiter got up more slowly and brushed at his clothes. His eyes had that faraway look that they always got when he was thinking.
“I was unable to move. A most interesting mental reaction,” he mused. “It’s similar to the way a small animal becomes paralysed when a snake looks at it. The animal literally can’t move, and is easily caught when it could have escaped.”
Bob and Pete both stared at their friend as he coolly analysed such a narrow escape from injury. Jupiter gazed up at the side of Devil Mountain in the moonlight.
“There seem to be many loose boulders up there,” Jupe observed, “and the mountain-side is very dry. I imagine it’s quite common for rocks to fall here. The naval gunnery probably loosened them in many places.”
The three boys approached the big rock. It was buried deep in the ground only a few yards from the entrance to El Diablo’s cave.
“Look, there are marks on it!” Bob was pointing at the boulder. “Gosh, Jupe, do you think someone pushed it down on us?”
“There are some marks,” Jupiter said after he had examined the rock more carefully. “Of course that is not so surprising.”
“It hit against a lot of other rocks on its way down,” Pete pointed out.
“We didn’t see anyone up there,” Bob said.
Jupiter nodded. “Still, someone up there might not want to be seen.”
“Gee, maybe we better go back,” Pete said.
“No, but we’ll be even more careful,” Jupiter said. “At least rocks can’t fall down a mountain at us when we’re inside the cave.”
With Jupiter in the lead, the boys entered the cave. They turned on their flashlights, and Bob marked the first question mark and arrow at the entrance.
Even with their flashlights on, they could see nothing but a long, dark passage that went straight into Devil Mountain. Its walls were smooth, and the ceiling was just high enough to permit Pete — the tallest investigator — to stand up. For a distance of about forty feet the passageway continued to be a straight tunnel with smooth stone walls. Then it suddenly opened into a large cavern.
The boys shone their flashlights all around the cavern. They were in a huge room with a towering ceiling. The far end of the cavern was so distant they could only just see it.
“It’s like a big city railroad station!” Bob exclaimed. “I never saw so big a cave.” His voice sounded hollow and faraway.
“Hello!” Pete called.
“Hello… hello… hello-ooooooo,” his voice echoed.
The boys laughed. The echoes seemed to bounce through the cavern. “Hello… hello-ooooo!” scouted Bob.
While Pete and Bob were shouting, Jupiter was inspecting the huge cavern more closely with the help of his flashlight.
“Look!” he suddenly called to them.
To their left, in the wall, was a small black hole—the opening of a passage that seemed to lead out of the cavern. The boys aimed their flashlights at the walls on both sides of the cavern. They saw many more openings — at least ten passages that led from the big cavern deeper into the mountain.
“Jeepers,” Pete said, “which way do we go?”
All the passages looked about the same — barely high enough for Pete to stand up in, and about four feet wide.
Jupiter frowned. “It is obvious that El Diablo’s Cave must be a large complex of passages and chambers all through the mountain.”
“Maybe that’s why the posse couldn’t find El Diablo,” Bob said. “There were so many passages that he could stay hidden.”
Jupiter nodded. “That seems a likely explanation.”
“How does a cave like this get started anyway?” Pete asked, looking around with awe.