Pete nodded. “Sure. It works both ways.”

Jupe pursed his lips. “Is it your own property, not a loan from the studio?”

“It’s ours, all right,” Pete said. “Or my Pop’s, anyway. Say, what’s all this about?”

“It’s about saving our lives — and possibly solving a mystery at the same time. Do you think your Dad would loan us your projector and the film you saw, just for tonight?”

Pete blinked. “You mean, to take out?”

“To take out,” Jupe repeated. “It sounds like the kind of picture I’d like to show somebody.”

Pete rubbed at his nose, and then shrugged. “I don’t know. I suppose so, Jupe. I’d have to phone him, of course, to get permission.”

“That’s great,” Jupiter said.

“Okay,” Pete said. “But before I try to convince my Pop of anything, I want to know where we are going tonight — and why. I’m tired of being in the dark.”

Bob nodded in agreement.

They both looked at Jupiter Jones. For a moment, he tried to disregard their stares. Finally, he shrugged and threw his hands open.

“Very well,” he said. “I was hoping to keep my clues and deductions a secret. Mostly because I’m not certain yet if they’re entirely correct. And even if they are, I’m still at a loss as to where they lead. This investigation started with trying to locate a missing dog. Since then, we have unearthed other mysteries. None of which appear to have anything at all to do with the mystery of the missing dog or dogs of Seaside. Mr. Allen hired us to find his dog, Red Rover. But I have felt from the start that the mystery of the other missing dogs would be cleared up when we found his. That was before we met the dragon.”

“What about the dragon?” Bob inquired. “You’ve made it pretty clear you think it’s a fake one. How come?”

“Yes,” Jupe said. “Even though I panicked and ran as you both did, I have several reasons for doubting the authenticity of the dragon in the cave.”

“Give us one, for a starter,” Pete said. “What makes you think it wasn’t real?”

“Several things. The cave wasn’t real. The old tunnel wasn’t real. The entrance to it wasn’t real. Naturally, given those things to consider, one is inclined to doubt that the dragon is any more real.”

“I didn’t notice any of those things,” Bob said.

“Start with the first cave we entered,” Jupe said. “We found some boards and moved one aside to enter the smuggler’s cave.”

“I remember you were looking at them in a funny way,” Bob said. “What wasn’t real about them?”

“It was supposed to be an old cave, a hideout for smugglers and pirates. The boards were old — at least some were.”

“Some?” Pete asked.

Jupe nodded. “The plank that we moved aside, for one. But there was a long, wide piece of plywood. Plywood, I don’t have to remind you, is a fairly recent process in manufacturing wood products. There wasn’t any available for pirates or even smugglers.”

“Plywood?” Pete repeated. Then he frowned, “Well, maybe. But it doesn’t sound like too much proof of anything.”

Jupiter went on. “Let’s take the next cave. The large one we discovered when Bob found the rock that moved. We still don’t know who made that possible. If you recall, we advanced into that cave inland, because there was no other way to go. No outside opening, no mouth to it like the first.

“Then we had to stop. We were confronted by what appeared to be a solid wall at the end. We had hoped this cave would lead to the old tunnel Bob had discovered in his research.”

Both his partners nodded.

“I remember you started to scrape away at it with your knife,” Pete said, smiling. “What did you find out, aside from the fact that solid rock can ruin a good knife blade?”

Jupiter reached into his pocket. He took out his pocket knife and opened it.

“Notice the grey particles on the blade,” he said. “Then smell them.”

Pete and Bob did as he suggested.

“Paint!” they both exclaimed in unison.

Jupe nodded, folded the knife, and put it away.

“Walls of old caves are not painted,” he said. “And as I scraped the covering away, my blade left a streak in the surface. In my opinion, the wall was not rock at all, but plasterboard — sprayed with a grey paint, with sand and small stones thrown roughly on to the surface to make it look like a real cave wall. Plasterboard is, you know, an industrial material commonly used for walls in houses, or partitions in offices. A lot of it is prefabricated, with built-in textures looking like cork or brick.

“I believe whoever put that wall up was trying to hide a fascinating and perhaps valuable discovery,” Jupe said.

“Like what?” Bob asked.

“Something more important on the other side,” Jupe said. “Something, I suspect, like the original old tunnel of the uncompleted rapid transport system!”

“That’s it!” Pete exclaimed. “Somebody discovered the old tunnel and then closed it up so that nobody else could find it! They thought a fake wall would turn away anybody who managed to get in that far.”

“Unless,” Bob added, “unless that’s the way they closed it up in the first place.”

“Prefabricated board isn’t fifty years old,” Jupe said.

“Maybe not,” Bob replied. “But we don’t know exactly when the tunnel was boarded up, either. Maybe they did it later. To keep kids and animals out.”

Jupe’s eyes were thoughtful.

“Possibly, Bob, although I doubt it. However, we now have to consider the third mysterious happening. We were at the wall. I was testing it, I turned to show you what was on my knife, and then — ”

Pete nodded, and gulped. “Then the cave opened up and it got lighter all of a sudden, and the dragon came in. I see what you mean.” He scratched his head. “At least, I think I do. Maybe you’d better tell me.”

“All right,” Jupe said. “The cave opened up. How did it open? What made that possible? There was no opening outside that we could see. Otherwise, we certainly would have entered that cave rather than the first one, where Bob fell into the mud-hole.”

“Okay,” Bob admitted. “We couldn’t see any opening. But the dragon knew about it, somehow. Because he managed to open it. Maybe he’s a lot smarter than we are.”

Jupe raised his hand. “Remember, my theory is based on my feeling that everything was false and contrived. Therefore, the dragon was, too. And if it’s smarter than we are, then it’s only because the dragon is not really a dragon, but something controlled by some human agency.”

Pete blinked. He turned to Bob. “What’s he saying?”

Bob shook his head. “I think he’s saying our dragon is a robot, not a dragon. Is that it, Jupe?”

“I’m not certain yet,” Jupiter admitted. “It may be a robot, or some construction similar to the dragon used by Mr. Allen in his old horror film. We’ll find out in due course.

“What I am certain about, however, is the cave entrance. That, too, was not real. Unfortunately, we never tested it or examined it closely from the outside. I’m sure that if we do, we’ll find it’s a fake entrance — built of some lightweight material, just as any fake film set or prop is, covered and painted to make it look real. Anybody could build a fake rock. Whoever did it covered the true entrance to the cave. When he wanted to enter, or wanted his dragon to enter, he merely moved the fake opening aside.

“I’m sure you’ll both admit,” Jupe added, “that if the city of Seaside wanted to cover up a big cave or a tunnel, they wouldn’t use any lightweight, painted boards inside and fake rocks outside. They would have sealed it up solidly — with concrete!”

Pete looked out of the window of the smooth-purring Rolls. He frowned, then nodded. “Maybe you’re right, so far. If we go back tonight, we’ll test those rocks near the first cave entrance. But rocks don’t scare me. What I want to know about is the dragon. Why wasn’t it real?”

Jupiter Jones sat back, folding his arms.

“We all saw it about the same time. We were about the same distance away. Our hearing and sight are all on a par. Now what did we hear? What did we see?”