“It means a man we never suspected is behind it all,” Jupe said. He shook his head ruefully. “It’s all perfectly clear now.”

“What are you trying to tell us now, Jupe?” asked Jim Hall.

“You won’t like it,” Jupe said. “It’s Doc Dawson.”

Jim Hall smiled thinly. “I don’t think you know what you’re talking about, son. Doc’s an old friend. Let me see that piece of paper.”

As he held out his hand, the front door opened.

A burly figure stood there. Head close-shaven, arm tattooed. “I came to pick up Doc’s bag,” he said. “He forgot it here.”

His eyes narrowed as he saw the open medical bag, and then the small slip of yellow paper in Jupe’s hand. His lips twisted angrily. “I’ll take that, you snooping kid!” he roared.

Before Jupe could move, Bo Jenkins had snatched the paper from his hand. He crumpled it in his huge fist and reached for the leather bag.

Jim Hall spoke up mildly. “Hold it just a second, Bo. There’s something going on here and — ”

Jenkins made a sudden movement and pulled out a gun. “Stay out of it, Hall, if you know what’s good for you. We got it all now and nothin’s stopping us.”

Jupe gulped. “You’re the man who bought all the cages from my uncle — and gave Jim Hall’s name!”

Jenkins grinned. “Wise apple, huh?”

Jim Hall whistled softly as the animal handler grabbed the black bag.

Heavy, padding steps sounded across the room. An ominous rumbling made Jenkins turn and stare. His jaw sagged and he paled.

A large, yellow-eyed lion stood there, head down and long tail twitching restlessly. The growling continued.

Instantly Jupe leaned against the door, closing it.

Jenkins whirled again at the sound, his gun jerking.

“Forget it, Jenkins,” Jim Hall said calmly. “You’re not going anyplace. One more step and George will have you for dinner.” Hall turned to the lion. “Won’t you, George?”

The lion slowly opened its cavernous mouth and moved forward.

There was a clattering sound as the gun fell from Bo Jenkins’s fingers.

“That’s better,” Jim Hall said. He bent forward to retrieve the gun and waved the frightened man to a chair. The lion came forward and stopped at Bo’s side, opening its mouth in a huge yawn.

“Now then, Bo,” Jim Hall said pleasantly. “What can you tell us about some smuggled diamonds?”

As they rounded a turn in the trail, Mike pointed ahead to a small house next to a barn. “That’s Doc Dawson’s place,” he said. “The dispensary is in the back.”

Sounds of hammering came from the barn.

Jupe smiled. “That’s one thing he never figured on. When my Uncle Titus has something fixed, he does a very thorough job.”

“What do you mean, Jupe?” asked Mike.

“You’ll see in a minute,” Jupe said mysteriously.

A small pickup truck stood in the driveway by the barn. Alongside it four cages lay tumbled on the ground. The grizzled vet stood next to one with a hammer raised in one hand. In the other he held a long pair of pliers.

He paused as Jim Hall strode up, flanked by the boys. His eyes nicked past them and narrowed.

“Howdy, Jim,” he said. “Anything wrong?”

Jim Hall shook his head. He tossed the black leather bag at the vet’s feet. “Heard you were looking for your bag, Doc. You left it at the house.”

“Thanks, Jim,” Dawson said. He gazed beyond them and frowned. “I sent Bo Jenkins — I thought — ” He looked at the cages, scowling. “I need him to help — ”

Hall nodded. “Bo’s all tied up at the moment, Doc. Maybe we can give you a hand. What’s the trouble?”

The vet looked at the hammer in his hand. “No trouble, Jim. Just wanted to make sure the bars are good and tight. Don’t want any more accidents. That fellow Eastland will have every nickel of yours if one more animal gets away.”

Hall smiled. “Thanks, Doc. I appreciate your concern.” He looked at Jupe. “Can you tell which bars?”

“I think so, sir,” Jupiter said. “But I’d need to borrow his hammer.”

“No problem,” Hall said. “Can you loan this young fellow your hammer for a moment, Doc?”

Dawson hesitated, then handed it to Jupe. “Guess so. What’s up?”

“These young fellows are The Three Investigators. I hired them, you recall, to find out what’s been making old George nervous. They’ve come up with some cock-eyed notion that it’s all because of some smuggled diamonds.”

Dawson grinned. “No kidding? Cock-eyed is right.” He looked at Jupe. “Any idea where they might be?”

“Yes, sir,” Jupe said. “If you would just step aside for a moment, please.”

“Why, sure,” Dawson said easily, moving away. “Only go easy with that hammer, son. I wouldn’t want those bars loosened after all the trouble I’ve been to tightening them up.”

“You didn’t tighten them up,” said Jupe. “Hans and Uncle Titus did, back at our junkyard.”

Doc looked surprised.

“You’ll notice,” Jupe continued, “they didn’t put back the bars the way they were. Uncle Titus is very fussy about giving a customer no reason for complaint. So he and Hans bolted and screwed the bars in this way so they wouldn’t work loose as they did before.”

“Very interesting,” Dawson said.

“So you can’t hammer them off,” Jupe said. “All you can use the hammer for is this, really.” He walked around the cage beating at the bars with the heavy hammer. He stopped at the fourth one from the end, then continued through the others, pausing once more. He returned to the fourth one again.

“There are two on this cage,” he said.

Dawson glanced at Jim Hall. “Any idea what he’s talking about?”

Hall frowned. “I’d rather wait and see, Doc.”

“Most of these bars are rusted,” Jupe said, “indicating they’ve been outside and exposed to the weather a long time. They could belong to any of the cages Mr. Hall discarded. But this rusty one gives off a different sound — it’s hollow, you see. So my deduction is this one could have come from George’s cage.

“This one here,” Jupe continued, striding to the opposite end of the cage, “is hollow, too.” He struck it with his hammer. “It’s still in good condition because it just came in recently. It’s from the gorilla’s cage. Bo Jenkins took it off the night the gorilla arrived. The gorilla twisted the other bars apart and broke out. I believe the gorilla went after Bo and he became frightened and ran, tossing the bar away in his panic. I happened to come across it by accident.”

“But how did Bo Jenkins know you had it?” Mike asked.

“He was out looking for it later that night,” Jupe said. “He heard us and pointed his torch at us and saw me holding it. He’d seen us before and probably Doc Dawson told him who we were and where we came from. He came to the yard and found my uncle working on the cages. He must have been delighted when he heard they’d have to search the yard for extra bars. He couldn’t be sure, but there was a good chance the gorilla bar would turn up. Of course, he had no idea that George’s bar was around, too.”

“How can you be sure you’ve found the right bars here?” asked Mike.

“I can’t, until we take the bars off,” said Jupe. “But I expect we’ll find the diamonds in them, since I used the smugglers’ own method of locating them.”

“How do you know that?” asked Mike.

“The cable told me, and Doc Dawson confirmed it. The cable said, ‘DOX ROX NOX EX REX BOX.’ Which means, knock on the bars of the lion’s cage and you’ll find the diamonds inserted at the docks. EX, I would guess, stands for ‘out of’ — take the lion out first. A wise precaution, considering what happened with the gorilla.

“Now, do you recall what Doc did last night when the gorilla was brought back? Doc tested all the bars on its cage with the hammer. He did the same thing with the panther cage. At the time it merely seemed an odd way to test the strength of bars. But Doc was actually testing for diamonds — probably trying to make sure Jenkins had picked the right bar, or possibly making sure there were no others. Once they had the manner of smuggling arranged and the cable informing them how to look for the hollow bars — it was easy. Any bar that sounded hollow would contain diamonds.”