The foreman’s eyes seemed to glow in the dark. “Indians always did say that no one could see The Old One!”

“Luke!” Mrs. Dalton cried.

But the foreman stood his ground. “I ain’t saying I believe the stories. But a man’s got to look straight at things. That cave’s started moanin’ again, but so far nobody’s found nothin’ to explain it. If it ain’t The Old One, what do you reckon it is?”

With that, Luke Hardin walked down off the porch towards the bunkhouse. Mrs. Dalton stared after him with a worried expression.

“I’m afraid this is affecting all of us,” Mrs. Dalton said. “Luke’s as brave a man as I ever saw. I never heard him talk that way before.”

“I wonder why he decided to talk to us about The Old One?” Jupiter asked thoughtfully.

Mrs. Dalton suddenly smiled. “I expect Luke’s just tired. We’ve all been worried and working too hard. Now, what do you boys say to some milk and cookies?”

“Yes, ma’am!” Pete answered quickly for all of them.

Soon the boys were eating cookies in the comfortable living-room of the old ranch house. Colourful Indian rugs covered the floor under the rustic hand-hewn furniture, and a large stone fireplace almost filled one wall. The mounted heads of deer, bear, and mountain lions hung on the walls.

“Just what is The Old One, Mrs. Dalton?” Jupiter asked, helping himself to another cookie.

“An old Indian legend, Jupiter, nothing more. When the Spaniards first came here a very long time ago the local Indians said that a black and shiny monster called The Old One lived in a pool deep inside the cave in Devil Mountain.”

Pete blinked. “But if no one could see The Old One, how did they know it was black and shiny?”

Mrs. Dalton laughed. “There, you see? Of course it doesn’t make sense. I suppose they believed that someone had once seen the thing and told others about it, and that’s how the story was handed down.”

“What did the Spaniards think?” Bob asked.

“Well, that was a long time ago,” Mrs. Dalton said, “and they were pretty superstitious, too. They said they didn’t believe it but they never went near the valley if they could help it. Only the very bravest, like El Diablo himself, went into the cave.”

“Can you tell us about El Diablo?” Jupiter asked.

At that moment Mr. Dalton entered the room, accompanied by a small, thin man who wore heavy glasses. The boys had met the man earlier. He was a house guest of the Daltons, Professor Walsh.

“Ah, boys, I hear that you have been out at our mysterious Moaning Valley,” said the professor.

“Foolishness!” Mr. Dalton snapped. “Nothing has happened there that doesn’t happen on any ranch. Simple accidents, nothing more.”

“Of course you’re right,” Professor Walsh said, “but I’m afraid your men don’t believe that. Uneducated people would rather believe in supernatural forces than in their own carelessness.”

“If only we could find the cause and show them,” Mr. Dalton said. “After this accident to-night I’ll lose more men. But even Jupiter here could see that the slide was caused by that naval gunfire off the coast.”

“Excuse me, sir,” Jupiter interrupted, “but we would like to help if we could. We’ve had some experience in this sort of thing, as Mr. Crenshaw may have told you.”

“Experience?” Mr. Dalton repeated, staring at the boys.

Jupiter produced two cards from his pocket and handed them to Mr. Dalton. The tall rancher studied them. The first, a large business card, said:

Mr. Dalton frowned. “Investigators, eh? Well, I don’t know, boys. The sheriff might not like boys interfering.”

Professor Walsh looked at the card. “Why the question marks, boys? Do you doubt your ability as detectives?”

The professor smiled at his own joke, but Bob and Pete only grinned and waited for Jupe to explain. Adults always asked about the question marks, which was exactly what Jupiter wanted.

“No, sir,” Jupiter said. “The question marks are our symbol. They stand for questions unanswered, mysteries unsolved, enigmas of all sorts that we attempt to unravel. So far we have never failed to explain any riddle we’ve found.”

Jupiter said the last proudly. But Mr. Dalton was looking at the second card, a small green one. Each of the boys had one, and they all read the same:

This certifies that the bearer is a Volunteer Junior Assistant Deputy co-operating with the police force of Rocky Beach. Any assistance given him will be appreciated.

(Signed) Samuel Reynolds

Chief of Police.

Professor Walsh peered at the card through his thick glasses. “Well, well. Very impressive, boys. You do indeed have fine credentials.”

“You boys certainly showed more sense to-night than half the adults around here,” Mr. Dalton said at last. “Maybe three boys with a fresh viewpoint are just what we need to solve this nonsense. I’m sure there’s a simple explanation, and if you promise to be very careful around that cave, I say go ahead and investigate.”

“We’ll be careful!” the boys cried in unison.

Mrs. Dalton smiled. “I’m sure there’s some very simple explanation we’ve all missed.”

Mr. Dalton snorted. “I say it’s the wind blowing through those old tunnels and nothing more.”

Jupiter finished the last cookie. “You and the sheriff have searched the cave, sir?”

“From one end to the other. Many of the passages are blocked by debris from old earthquakes, but we searched every one we could find.”

“Did you find anything that looked as if it had changed recently?” Jupiter questioned.

“Changed?” Mr. Dalton frowned. “Nothing we could see. What are you getting at, son?”

“Well, sir,” Jupiter explained, “I understand that the moaning only began a month ago. Before that it hadn’t been heard for at least fifty years. If the wind is causing the sound, then it seems only logical that something must have changed inside the cave to make the moaning sound start again. I mean, I doubt if the wind has changed.”

“Hah!” Professor Walsh said. “There’s clear logic, Dalton. Perhaps these boys can solve your mystery.”

Jupiter ignored the interruption. “I also understand,” he went on, “that the moaning occurs only at night, which would not be the case if the wind alone were responsible. Have you noticed if it happens every windy night, by any chance?”

“No, I don’t think it does, Jupiter,” Mr. Dalton was beginning to look really interested. “I see what you mean. If it were just the wind, then we should hear moaning every windy night… Of course, it could be a combination of wind and some special atmospheric condition.”

Professor Walsh smiled. “Or it could be El Diablo, come back to ride again!”

Pete gulped. “Don’t say that, Professor. Jupe already said the same thing!”

Professor Walsh looked over at Jupiter. “He did, did he? You’re not going to tell me that you believe in ghosts, are you, young man?”

“No one knows about ghosts for sure, sir,” Bob put in seriously. “However, we’ve never actually found a real ghost.”

“I see,” the professor said. “Well, the Spanish people have always insisted that El Diablo will come back when he is needed. I’ve done a great deal of research, and I can’t really say that he couldn’t come back.”

“Research?” Bob asked.

“Professor Walsh is a professor of history,” Mrs. Dalton explained. “He’s here in Santa Carla for a year to do special research on California history. Mr. Dalton thought he might be able to help us explain Moaning Valley to our ranch hands.”

“With no luck so far,” the professor admitted. “But perhaps you boys would be interested in the full story of El Diablo? I’m thinking of writing a book on his colourful career.”

“That would be great!” Bob exclaimed.