Jupe glanced up at the lighted house. “You said somebody must have let him out before. Couldn’t it happen again?”

Mike put his hand in his pocket and produced a key. “This time the house is locked. Only Jim and I have keys.”

Jupe pondered. “You’ve told us, Mike, that George becomes nervous and restless at night. I suggest we walk round to see if we can’t uncover some reason for his nervousness. We should explore the area closest to the house to begin with.”

“Swell,” Mike said. “As you can see, the house is set in a clearing on this knoll. Over there’s a shed for tools and firewood. It could be a garage but Jim parks outside here. The road at the foot of the drive leads north and runs into other roads.”

He led the boys around the area. The night was quiet after the earlier excitement. The moon was now up, and the sky was cloudless.

Jupe nodded as if satisfied when they completed their circuit of the house. They returned to the cage area. The gorilla cage remained empty. The panther in the other lay quietly, switching its long tail and watching them balefully.

The Three Investigators followed Mike down the hill into the jungle. “I’ll explain Jungle Land as we go along. Then the next time you come, you’ll know your way around here without me.”

“How big is Jungle Land?” asked Bob. “It seems with so much land to cover, you’d never know what’s going on.”

“It’s about a hundred acres, and diamond-shaped. That’s a lot maybe, but we’ve never had any trouble keeping track of things before.”

“Where is the Jay Eastland movie being shot?” Pete asked.

“North of here, about a five-minute ride,” Mike said. “We’re heading due east now, towards our closest border fence.”

The trail descended steeply through brush, rocks and fissures. Faint patches of moonlight showed between trees.

“Where’s the canyon your uncle said the gorilla was seen at?” asked Bob. “He seemed to be heading north, too.”

“He was, but he’ll cut left on another road. The canyon is north-west, about fifteen minutes away. Just below it, we have several acres that look like the African veldt, grassy and flat. We have the elephants there, contained by a moat, so they can’t get out. But you can hear them trumpeting.” He grinned. “I like that sound.”

“I like it better myself now,” said Pete, “knowing they can’t get out.”

Mike continued to describe Jungle Land as they went on downhill. “At the far west end opposite us is the built-up tourist section. Our main attraction used to be the jungle and animals, but a lot of folks seem to prefer the Wild West. So we have a frontier town, a mock graveyard, a ghost town, and a stagecoach ride for the kids. We keep the horses pretty near that area.

“In the southern part is the entrance where you come in, and lots of jungle. In the central part is the lake and then above that, where Eastland is, more jungle. At the northern end are mountains, with one high precipice. It’s been used for a lot of movies where the hero has to dive off a cliff. Doc Dawson has his dispensary up that way.”

There was an outburst of chattering cries and hoots. The boys stopped and looked at their guide.

“Those are monkeys and owls,” Mike explained. “We’ve also got a snake-house in the north-east section but the snakes don’t make any noise. We keep them farthest away because they’re the hardest to find in case they ever get away. We’ve a good collection of sidewinders — they’re rattlesnakes — and a water moccasin and a good-sized king snake.”

Jupe was peering intently back through the trees. “How far are we from your house now, Mike?”

“About five hundred yards. There’s a fence down the end of this slope here — ”

“Wait!” Pete whispered. “What’s that?”

They all heard it then. A slow, dull, crunching sound echoing with a measured beat. The Three Investigators looked at each other. The crunching sound became louder, seeming to come closer. Prickly chills ran down their spines. Then they heard a new sound. It started as a low whine and began to rise on a shrill, insistent note.

“I don’t like that,” Pete said hoarsely. “Maybe we ought to be getting back — ”

Jupiter’s eyes were wide with fear, too, but they were also puzzled. “That sound — ” he started to say. “It — it’s — ”

As he groped for words, the shrill, whining noise ascended to a full-noted shriek. The screeching seemed to be all around, engulfing them.

EEEE — ooo — EEEEE! EEE — ooo — EEEEE!

Bob yelled, “I’m getting out of here!”

With one mind, The Three Investigators wheeled and ran.

“Wait!” Mike called.

They turned to stare in utter amazement.

Mike Hall was laughing.

“It’s nothing to worry about,” he called. “That’s only the metal shredder!”

The shrill, wailing sound slowly fell until it became a low, whistling note.

“Metal shredder?” Jupiter repeated dumbly.

Mike was pointing ahead through some trees. “Yes, Jupe. Over the fence, the other side of our property. There’s a salvage yard — steel and scrap iron. It’s full of scrapped cars and other junk.”

“What does the metal shredder do — besides scare people?” Bob asked.

“It’s a new recycling process to salvage precious metal,” Mike said. “Part of the new ecology drive. The cars used to be just pounded down and sold as scrap iron and steel. But now they have this new device — some kind of claw with a computer-selector-processing operation. It shreds the cars into little bits. The metal is separated from the other material, and then the more precious metals, like copper, are separated from the iron and steel.”

“Whew!” Pete exclaimed weakly. “Is that all? It sounded like all the gorillas in town were holding a convention!”

Jupe was plucking at his lower lip. He glanced at his wristwatch.

“It is now nine thirty,” he stated. “Does George usually become nervous and restless about this time, Mike?”

Mike shrugged. “Sometimes sooner or later. I don’t know exactly what time — except that it’s always after it gets dark.”

“Always at night? Never during the day?”

“Never,” Mike said firmly. “But I’m not counting this afternoon. George wasn’t nervous then — just acting mean. I’d say because he was hurt.”

“What’s your idea, Jupe?” Bob asked. “That the sound of the metal shredder made George nervous?”

“Animals are more sensitive to sounds than humans,” Jupe said. “Perhaps George is reacting to that high whine of the metal shredder.”

“ But he’d hear it all the time then,” Pete put in. “Not just at night.”

“A good point. Second,” said Jupe, “does this metal-shredding process operate during the day, too, Mike?”

“Sometimes,” Mike said. “Off and on again. I don’t pay much attention to the sound any more. It isn’t nearly as loud up by our house.”

“Hmmm,” Jupe said. “How long has that machine been in operation?”

“It’s kind of new, Jupe. The scrap yard has been here a long time, a number of years. And the wrecking part of it, also. But offhand my guess is they haven’t been using this metal shredder more than a month.”

“A month,” Jupe repeated. “And how long has George been acting nervous and restless?”

“Since about two or three months ago,” Mike said. “I remember it started just before the rainy season when Jim decided to bring George inside the house for good.”

Jupiter scowled, puzzled.

“Don’t forget, he didn’t act up every night,” Mike added. “He was restless at times, then seemed to be all right. But the last week or so, he’s been getting much worse, and it’s been regular since.”

“So he was nervous before the metal shredder came in,” Bob said.

Jupe looked thoughtful. “It would seem that George isn’t used to being cooped up indoors at night. That might account for his actions. The metal shredder could be a factor, or perhaps not. There could be different reasons.”