The sound of jingling carried across the night along with the clip-clop, clip-clop, clip-clop of a horse’s hoofs.
“Oh no!” Bob groaned.
“Is that what we heard inside the cave?” whispered Pete.
“I think so,” Jupiter said. “The sound must have filtered down through some crevice in the rock of the mountain. Sound carries very clearly that way. It would have seemed as if it was inside the mountain itself.”
The boys crouched down in the thick bushes near the gate as the hoof beats came closer. Then a great black horse appeared on the steep slopes of Devil Mountain. It came down the mountain at a trot and passed within a few feet from where the boys crouched in the bushes.
“There’s no rider!” Bob whispered.
“Should we try to catch it?” asked Pete.
“No, I don’t think so,” Jupiter replied. “Let’s wait.”
The boys crouched silently under cover of the bushes. Suddenly Pete stiffened, and pointed towards the slope. A man was coming down the mountain at a fast walk. As he passed their hiding place, they had a clear view of him in the moonlight. He was a tall, dark man with a long nose, a ragged scar on his right cheek, and a black patch over his right eye!
“Did you see that eye patch?” hissed Pete.
“And the scar,” Bob added.
“I was more interested in his suit,” Jupiter whispered. “It was definitely a business suit, and unless I am mistaken I think he had a pistol under his coat!”
“Can’t we go now, Jupe?” said Pete nervously.
“Yes, I think we’d better,” Jupiter agreed. “This has been a most interesting night.”
Pete and Bob needed no urging. As they hurried along the road to where they had left their bikes, they kept looking behind them anxiously. But they saw nothing else. While they were riding past the end of Moaning Valley, however, a long wail echoed through the night.
Pete sat up quickly, bumping his head on the low ceiling.
“Ouch!” he grunted.
“Shhhhhh!” Bob hissed from his bunk across the room, and pointed towards the window.
In front of the window Jupiter sat cross-legged on the floor, looking like a small Buddha in his bathrobe. A large sheet of paper was spread out on the floor in front of him and in the middle of it he had stacked four books. On the paper Jupiter had drawn a lot of pencil lines.
As Pete stared down at the books and the paper and the pencil marks he realized that Jupiter had made a rough model of Moaning Valley. He had marked the cave entrances in pencil.
“He’s been sitting like that for an hour,” Bob explained.
“Gosh,” Pete said. “I couldn’t sit like that for ten minutes!” The intense concentration of their stocky friend always awed Bob and Pete.
Suddenly, Jupiter spoke. “I am ascertaining the exact topographical arrangement of Moaning Valley, Pete. The key to our puzzle lies in the physical pattern.”
“Huh?” Pete said.
“Jupe means that he thinks the mystery can be solved by studying the lay of the land,” Bob explained.
“Oh,” Pete said. “Why didn’t he say so?”
Ignoring Pete, Jupiter went on, “The real mystery of Moaning Valley is why does the moaning stop when we go inside? It happened twice last night, yet when we were leaving the area the moaning began again.”
He held up a newspaper. “I have here a newspaper report of the sudden recurrence of the moaning. In it the sheriff says that the main reason no one has been able to identify the cause of the moaning is that once inside they never hear it any more.”
Jupiter put down the paper. “I’m convinced now that the moaning doesn’t stop by accident!”
“I guess you’re right,” Bob said. “The way it started again right when we were leaving sure looks like someone was watching us.”
“But how does that — uh — model help us, Jupe?” Pete blurted out.
Jupiter looked down at his crude model. “I’ve marked all the places we were last night. Now we know that both times we entered the cave the moaning stopped instantly. It happened too quickly for it to have been someone inside the cave who was watching us.”
Bob nodded eagerly. “I get it! So we had to be seen before we went in.”
“Exactly,” Jupiter said, “and from my model I’ve deduced that we could have been seen everywhere we went from only one place — the top of Devil Mountain.”
“Then all we have to do is tell Mr. Dalton someone is up on Devil Mountain and let him catch the person!” exclaimed Pete.
Jupiter shook his head. “No, Pete, no one would believe us unless they caught the man and it would be almost impossible to get to the top without being seen. Whoever is up there would just run away.”
“Then — ” Bob began.
“How — ” Pete started at the same instant.
“We will have to observe what is actually happening in the cave,” Jupiter said solemnly, “so that we can tell people the full story.”
“But we don’t know what’s happening in the cave,” Pete objected. “Do we?”
“No, but I’ve got a plan in mind,” revealed Jupiter, “and I’ve got a clue as to what it’s all about!”
“You do?” Pete said. “What is it?”
“Last night I found this in one of the passages,” Jupiter explained, holding up the rough, blackish stone he had found in the mine-shaft passage. “The passage was once a mine shaft, and I found this stone just where it ended in one of those blockages.”
Bob took the little stone, looked at it with a puzzled expression and passed it on to Pete.
“But what is it, Jupe?” Pete demanded. “I mean, besides a kind of hard, slippery stone?”
“Scratch the window with it,” Jupiter said.
“What?” Pete said, surprised. “You know it won’t — ”
“Go ahead,” Jupiter urged, a smug expression on his round face.
Pete went to the window and scratched the small stone over the glass. It cut into glass almost as easily as a knife cutting into butter. Pete let out a low whistle.
“Jupe!” Bob exclaimed. “You mean that’s a — ”
“Diamond,” Jupiter finished. “Yes, I think that’s exactly what it is. A rough, uncut diamond. And a pretty big one. I think its quality isn’t good, probably no more than an industrial stone. But it is a diamond.”
“You mean El Diablo’s Cave is a diamond mine? Here in California?” Bob asked sceptically.
“Well, there have been rumours, I think, and — ”
That was as far as he got. A vigorous knock on the bedroom door interrupted him, and Mrs. Dalton’s voice called, “Up and at ’em, boys! Breakfast’s on the table. We’ll have no late sleeping here!”
Everything else was forgotten for the moment as the boys realized how hungry they were. They dressed and were in the big ranch kitchen five minutes later. Mr. Dalton and Professor Walsh smiled at them.
“Well, I see that Moaning Valley and its mystery have not affected your appetites, boys,” Professor Walsh commented.
Mrs. Dalton bustled around the roomy, bright kitchen and soon the boys were digging into stacks of buckwheat cakes and ham, and drinking mugs of cold fresh milk.
“You boys ready to do some work today?” Mr. Dalton asked.
“Of course they are,” Mrs. Dalton said. “Why not take them up to the north meadow for the haying?”
“Good idea,” Mr. Dalton agreed. “Later they can help round up some mavericks.”
The boys, who had done some reading on ranch life, knew that “mavericks” were cattle that had strayed from the main herd into remote parts of the range.
“Did you boys have a good walk on the beach last night?” Professor Walsh asked. “What did you find?”
“We had an interesting expedition,” Jupiter answered. “And we met a rather odd old man. He called himself Ben Jackson. Who is he, sir?”
“Old Ben and his partner, Waldo Turner, are prospectors,” Mr. Dalton explained. “I imagine they’ve looked for gold and silver and precious stones all over the West in their day.”
“According to local gossip they came here many years ago,” Mrs. Dalton added, “when there was a rumour that gold had been found. Of course, there never was any gold, but apparently Old Ben and Waldo never gave up. They have a shack on our land, and still consider themselves prospectors. They don’t seem to like to have visitors, but they don’t mind getting handouts from the ranchers around here. Of course, we call it a grubstake. They wouldn’t take charity.”
“They’re quite famous local characters,” Professor Walsh put in.
“They can really tell you stories,” Mr. Dalton smiled, “Of course, they’re somewhat eccentric, and most of their stories are just tall tales. For example, they’ll tell you about fighting the Indians, but I doubt if they ever did.”
“Gosh, you mean all that was a lie?” Pete exclaimed.
Before Mr. Dalton could reply, the back door of the kitchen burst open. The foreman, Luke Hardin, came in hurriedly.
“They just found young Castro out in Moanin’ Valley,” Hardin said grimly.
“Castro?” Mr. Dalton looked worried.
“Got thrown from his horse last night while he was riding herd on some strays. Lay there all night,” said Hardin.
“Is he all right?” Mrs. Dalton asked.
“Doc says he’s okay. They took him over to the hospital in Santa Carla.”
“I’ll go and see him right away!” Mr. Dalton jumped up.
“The men are kind of shook up,” Hardin added, his face dark. “Two more told me they’re going to quit. Castro was out in Moanin’ Valley and says he saw something moving. He took a look. Whatever it was spooked his horse. He was thrown and the horse ran off. He’s all bruised up and his ankle’s sprained.”
The Daltons looked at each other in despair. Jupiter spoke up.
“Was the horse a big black one, Mr. Hardin?” he asked.
“That’s right — Big Ebony. A good horse. Came back to the corral on his own this morning, so we knew to look for young Castro.”
Mr. Dalton spoke sharply. “Did you boys see Big Ebony last night?”
“Yes sir,” Jupiter said. “A big black horse without a rider.”
“You must always report a riderless horse on a ranch, boys,” Mr. Dalton said severely. “We would have found Castro sooner.”
“We would have, sir,” Jupe explained, “but we saw a man following him and assumed that he was the rider. He was a tall man, with a scar on his right cheek and an eye patch.”
Mr. Dalton shook his head. “Never heard of a man like that.”
“Tall and an eye patch?” Professor Walsh inquired. “Sounds menacing, but definitely not El Diablo, eh? He wasn’t tall, and he didn’t wear an eye patch.”
Mr. Dalton started for the door. “Luke, get the men calmed down if you can. I’ll join you in the north meadow after I see Castro. And I think I’ll talk to the sheriff about that man the boys say they saw.”
Jupiter spoke up again. “If you’re going into town, sir, perhaps you would take me? I have to return to Rocky Beach today.”
“Why, Jupiter, you’re not leaving us?” Mrs. Dalton asked.
“Oh, no,” Jupiter assured her. “It’s only that we need our scuba equipment. We saw some reefs offshore last night which look excellent for collecting specimens for our marine biology studies.”
Bob and Pete stared at Jupe. They did not remember that they had, seen any reefs, or that they were conducting marine biology studies. But they said nothing. They had learned not to question Jupiter when he had some scheme in mind.
“I’m afraid I don’t have time today to take you down,” Mr. Dalton said, “and I can’t spare a man or a truck. You’d better wait a few days.”
“That’s quite all right, sir,” Jupiter said. “If you’ll take me into town I’ll get the bus down. Someone will drive me back.”
“Better hurry up and get ready, then,” Mr. Dalton told him as he went out the door.
Mrs. Dalton looked at Bob and Pete. “I’m afraid you boys had better find something to do, too. With this trouble, Mr. Dalton won’t have time to work with you today.”
“We will, ma’am,” Bob assured her.
The boys went back to their room while Jupiter gathered what he needed for his return to Rocky Beach. As he packed, he revealed what he had in mind for Bob and Pete while he was gone.
“I want you to go into Santa Carla and buy a dozen large, plain candles,” Jupe said, “and three Mexican sombreros. With the Fiesta in Santa Carla there should be plenty of hats to buy. Tell Mr. and Mrs. Dalton you are going in to see the Fiesta parade.”
“Three sombreros?” Pete repeated.
“Right,” said Jupiter, without further explanation. “Then go to the library. Bob, I want you to learn all you can about the history of Devil Mountain and Moaning Valley. I mean all the exact details, not just legends.”
“I’ll find out all I can,” Bob assured the First Investigator. “What are you really going to Rocky Beach for?”
“To get the scuba equipment, as I said,” Jupiter replied, “and to take the diamond into Los Angeles to have it examined by an expert.”
Mr. Dalton called from below. “Jupiter! Ready?”
The boys hurried down, and Jupiter climbed into the cab of the pickup truck. As Bob and Pete watched him ride off, they realized that they still didn’t know what Jupe was planning to do with the scuba equipment.
After helping Mrs. Dalton in the kitchen for an hour or so, Bob borrowed Mrs. Dalton’s library card, and the two boys started off for Santa Carla on their bicycles.
“Enjoy the Fiesta, boys!” Mrs. Dalton called after them.
Actually, Bob and Pete were quite excited at the prospect of seeing the famous Santa Carla Fiesta, and they rode off in a holiday mood. The road from the ranch wound through the vast inland valley, surrounded on three sides by the brown mountains of Southern California. Away from the sea the sun was hot, and the boys noticed that all the creeks they passed were dry. At one point they crossed the wide bed of the Santa Carla River itself. Down below the bridge, the river bed was completely dried up, with small plants growing on its sun-baked surface.
Soon the highway began to climb towards San Mateo Pass. Bob and Pete had to get off their bikes and walk them around hairpin curves. Mountain valleys yawned close to the right, while rocky cliffs climbed steeply to the left. The boys walked slowly in the bright sun. After a long, hot hike they finally emerged at the top of the pass.
“Golly! Look at that!” Pete cried.
“Wow!” exclaimed Bob almost at the same moment.
Spread out before their eyes was a breathtaking panorama. The mountains sloped away to low foothills and then a wide coastal plain that spread in all directions to the blue water of the Pacific Ocean. The city of Santa Carla shimmered in the sun, its houses like tiny boxes in the great green expanse. Boats moved on the blue surface of the sea, and the mountainous Channel Islands seemed to float in the distance.
The boys were still staring at the magnificent sight when they heard thundering hoofbeats behind them. They whirled to see a horseman galloping down the highway straight at them. He rode a great black horse with a silver-mounted bridle and a silver-trimmed charro saddle, its enormous pommel horn glinting in the sun.
The boys stood transfixed as the horse bore down on them. The rider was a small slender man with dark eyes who wore a black sombrero, a short black jacket, flared trousers, and a black bandanna over the lower half of his face. He carried an ancient pistol that was aimed straight at the boys.