“Golly, Jupe, we could walk around in here for ever!”

“Yes, but, I’m sure we’re on the right track. The moaning gets louder every time we move east.”

Reluctantly Pete followed him into the third passage. The air current was strong and the moaning much louder. The tunnel went straight east! Jupiter pushed ahead as fast as was safe with only their flashlights. Suddenly both boys stopped in their tracks.

There was a gaping hole in the left wall, where a side passage joined the tunnel they were in.

“Gosh,” Pete said, “that’s the first side tunnel we’ve seen.”

“Yes,” Jupiter replied, examining it with his flashlight, “and it’s manmade — an old mine shaft that wasn’t sealed at this end. Pete, look!”

The flame of Jupiter’s candle was blowing strongly outward.

“What does that mean, Jupe?”

“It means,” Jupiter whispered excitedly, “that somewhere down there is a third opening to the outside! Probably one of the old mine entrances has been secretly opened.”

“Then why didn’t the sheriff find it? Or Mr. Dalton?”

“I’m not sure, Pete,” Jupiter admitted, “but — ” His eyes suddenly widened as he listened to something.

Then Pete heard it, too — a faint sound of digging.

“Come on,” Jupiter whispered, and started into the new passage.

As Pete prepared to follow, he suddenly became aware of the sound of footsteps behind him.

“Jupe,” he quavered weakly.

Standing there, close behind them, was a small, thin man with burning dark eyes and a proud face — the face of little more than a boy. He wore a black sombrero, a short black jacket, a high-necked black shirt, and tight black trousers that flared at the bottom above shiny black boots.

He was the young man in the picture Professor Walsh had shown them at the ranch. El Diablo!

And he held a pistol in his left hand.

“Yipes!” cried Pete.

El Diablo pointed his pistol at Pete and made a sharp cutting motion in the air with his other hand.

“He wants us to be silent,” Jupiter said, a little shakily.

El Diablo nodded. His boyish face showed no expression at all. He motioned with the pistol that he wanted the boys to walk ahead of him in the direction from which they had come, away from the sound of digging.

Reluctantly the two boys obeyed. They retraced their steps through the dark tunnel until they came to a cavern, where El Diablo motioned them to the right.

They walked and walked, along passages and through caverns. Although Pete knew by his watch that they had travelled for less than five minutes, it seemed more like five hours as he plodded along behind Jupiter. El Diablo, with his pistol, stayed just behind them.

“Halt!”

The command came sharply just as Pete and Jupiter entered another cavern. It was the first word El Diablo had spoken and it had a muffled, hollow sound.

The boys stopped. This cavern was smaller than most they had been in, and it had a gloomy, dank atmosphere.

“There!” El Diablo commanded in his muffled voice.

The bandit gestured towards a very narrow opening in the cavern wall. Jupiter and Pete looked at each other grimly, but there was nothing they could do. They marched into the narrow tunnel, with El Diablo close behind. They had taken only about ten steps when they came to a mound of rocks that completely blocked the passage. A dead-end! Pete and Jupiter turned in dismay.

El Diablo’s face was as rigid as stone. With a motion of his pistol, he indicated that they were to stand along the left wall. Then he quickly bent over and rolled a large rock away from the mound.

“Come!” the muffled voice commanded.

The boys walked to the hole that had been opened in the end of the passage, and Pete peered in. He saw nothing but a black hole. Before he could shine his flashlight inside, a strong shove sent him sprawling into the dark opening.

Pete landed hard on a stone floor. Something struck him in the ribs, and then he heard the stone being rolled back. Pete lay in total darkness behind the wall of rock.

“Pete?” It was Jupiter’s voice beside him.

“I’m here,” Pete answered, “but I wish I wasn’t.”

“I’m afraid he’s walled us in,” Jupe whispered in the darkness.

“I’m just plain afraid,” Pete said.

At the edge of Moaning Valley, Bob was hurrying towards The Crooked-Y Ranch. Behind him, as if to spur him on, the valley continued to moan.

“Aaaaaahhhhhhhh — oooooooo — oooooo — oo!”

Bob knew this meant that Jupiter’s plan had worked. Pete and Jupe must be inside El Diablo’s Cave by this time, yet the moaning had not stopped. After reading the book, however, Bob was almost sorry that the plan had succeeded. If his hunch was right, if Old Ben and his partner had something to do with the moaning sound, then Pete and Jupe could be in trouble.

Then there was the man in the car with the Nevada licence plate. Who was he? Bob had seen only a dark shape walking towards Devil Mountain. He had waited for a time near the car, but the man had not come back. Bob had finally decided that too much was happening for the boys to carry on alone.

He hurried on towards the ranch. Once Moaning Valley was behind him, Bob decided to risk walking on the road, where he could make better time. Gradually the moaning faded in the distance. Then he heard a new sound behind him. A car was coming fast along the narrow dirt road. Just in time, Bob jumped for the cover of the bushes at the side of the road.

As the car roared past, he could not make out the face of the man bent close over the steering wheel, but he saw a black sombrero on the head. He also saw that it was the car with the Nevada licence plate!

Alarmed, Bob hurried back on to the road. The Nevada car had been in a hurry. What had happened inside Devil Mountain? With a sinking feeling, Bob began to trot as fast as his injured leg would let him. He had to get to the ranch house right away. Maybe even Jupiter had gone too far this time.

“Uf — ooof!”

Bob had bumped headlong into a man who appeared suddenly in the road. Strong hands gripped his shoulders. He looked up into the long, scarred face of the man with the black eye patch.

Jupiter and Pete crouched in the darkness behind the wall of rock. From time to time they could still hear the moaning of the cave, distant and faint.

“Can you see anything?” Pete whispered.

“Not a thing. We’re totally walled in, and — Hey, are we crazy or something!” Suddenly Jupiter started to laugh.

“Gosh, Jupe, what’s so funny?” Pete whispered.

“We’re whispering,” Jupiter said, “and sitting in the dark, but there’s no one to hear us and we have our flashlights!”

The boys switched on their flashlights and grinned a little sheepishly at each other. Then Pete shone his light on the wall of rock.

“Maybe no one can hear us, and we have our lights, but how do we get out?” Pete asked.

Jupiter, as usual, refused to be discouraged. “First we’ll see if we can push that big rock out. El Diablo did not appear to be exceptionally strong, yet he moved the stone with ease.”

Pete tried to move the stone first. It would not budge. Then Jupiter joined him, and together the two boys applied all their strength. The boulder still did not move an inch. Panting, they finally gave up.

“He must have it wedged from the outside,” Jupiter observed. “The more we push, the tighter we wedge it. He’s locked us in tight.”

“Great,” Pete said. “What do you think. Jupe? Could he really be El Diablo? You know, the professor said he might still be alive.”

“El Diablo may still be alive,” Jupiter said, “but he wouldn’t look like that. Remember, El Diablo would be almost a hundred years old. The man who caught us looked like El Diablo back in the 1880s!”