176 .

Kirby stared, puzzled, while Ramonez simply shook his head. It was Bortha who spoke up, suddenly.

"I did," he said. Turning his head, Bortha glared at Mr. Brewster. "I wanted to know if you had arrived in Mexico City, so I could plan about going to Arista's museum. I couldn't give my name, so I talked like Tizoc, to throw a scare into anyone who answered."

"Then you planted the crystal skull?"

"Yes, a few hours earlier. I knew that Kirby had been snooping around the Del Monte, so I decided that would be something to pin on Kirby, too."

"Everything gets pinned on me," retorted Kirby, "and the biggest thing of all is this big pile of boxes." He turned to Ramonez. "What's in them, to make them so all-fired important?"

Ramonez turned to his deputies and said: "Show him."

They opened the boxes, and the boys moved forward to take a look with Kirby. One box was packed with rifles. Another contained machine guns. More boxes were opened, revealing more such weapons.

Ramonez turned and gestured to a still larger stack as he declared: "Those contain ammunition, actually millions of rounds of it. In that far stack, you will find thousands of hand grenades. Some boxes contain bazookas and other weapons. Enough to equip a small army."

Mr. Brewster spoke, somewhat puzzled: THE FINAL RIDDLE 17X.

"What did Bortha want to do? Start a revolution here in El Cielo? Why, he'd be crazy-"

"But he isn't crazy," interposed Ramonez, staring steadily at Bortha as he spoke. "He planned, as Tizoc, to make this cavern into an a.r.s.enal from which he could ship arms and ammunition to trouble-makers in any Caribbean countries where revolts could be stirred up. It is all part of an international plot, and he is an important member of it. As an archaeologist- which he is-he could turn up in any part of the world without causing comment."

"But how did he intend to ship the weapons out?"

Before Ramonez could reply, Bortha spoke for himself.

"By plane," he announced. Then, sneeringly, he went on: "Why do you think I kept telling Dr. La Vega that we needed a landing strip at El Cielo? So I would have it when I really needed it. I knew that time would be running short, sooner or later-"

"And fortunately," put in Mr. Brewster, "it happened sooner instead of later."

"That leaves just one thing," added Ramonez. "How Bortha planned to pay for all these arms. There can only be one answer. He must have found the lost Aztec treasure."

Bortha's broad face tightened suddenly with an expression of restrained fury.

"I feel sure you found it, Bortha," continued Ra- 178 .

monez. "That's why you engineered that cave-in. You are still hoping that you can get away with some of it. Instead, you are going to turn it over to us-immediately-"

Right then, Bortha made a sudden break. He whipped away from Mr. Brewster's grasp, drove hard at Kirby, and reeled the big man into Ramonez' path. With a quick recoil, he darted the other way, reached the corner of the cavern and pressed a hidden switch. A slab pivoted in the wall and in another moment, Bortha would have gone through the opening, locking the door behind him.

But in that moment, Biff and Mike had acted. To them, Bortha's quick darts were like the shifty tactics of a runner on a football field. They had gone after him and were guessing each twist that he intended. Now, Biff caught Bortha with a low tackle at the knees and Mike landed squarely on his toppling shoulders, flattening him solidly.

The revolving panel closed. Bortha's attempted escape had failed. Now Ramonez arrived, pressed the switch, and reopened the rocky slab. This time, they all went through, taking Bortha with them. Inside, they found a steep, zigzag stairway, its stone steps, all of ancient origin, leading deep down through the cliff.

By the time they had reached the bottom, they realized they were below the level of the excavation. There, the stairway opened into a huge, vaulted room, THE FINAL RIDDLE 179.

that was utterly fabulous in its glitter. All about were stacks of gold, in the form of plates, bowls, vases, statues, even weapons and suits of armor. All were the work of ancient craftsmen, and some of the decorated bowls and helmets were heaped to the brim with pure gold dust.

Jewels, too, were abundant. There were great mosaics, done in jade and turquoise, priceless in their own right. There were rings, bracelets, even crowns, set with amethysts, opals, and other valuable gems. Biff and Mike looked at each other, recalling the tales that they had heard of Montezuma's treasure and the wealth of other Aztec rulers.

This reality outmatched those fables.

Across the treasure room was a low archway, with a short, steep stairs beyond. At the bottom of these steps, the party reached a shaft of daylight and found themselves at the bottom of the deep pit that Bortha had dug into the rubble, within the fenced enclosure. They clambered up a ladder at the side of the pit and came out near Bortha's tent.

Bortha had gone up the ladder willingly and now, at the top, he gave a shrill cry, waving the arms of the Tizoc robe that he still wore. He was hoping that some of his followers posted there would make a last-moment rescue. But none of those followers was still around.

"I had my men take care of your crew," Ramonez ISO .

informed Bortha. "You'll find them when we put you in the local calaboose. From the way you moved around, we figured you must have two ways in or out, up or down, wherever you went."

Mr. Brewster was among the last to come up from the pit. Kirby had stayed down there with him, and both had gained a good look at the excavation work.

"It was exactly as I thought," Mr. Brewster told Ramonez. "Bortha had the props fixed for a quick knockout. He wanted to get rid of Dr. La Vega so he could take over the work."

"And it wouldn't be very hard to drop that rubble back into the pit," added Kirby. "Bortha was all fixed to clog it up again, if anyone came close to finding the treasure."

Later, at the Hotel Pico, they found Dr. La Vega well enough to hear the news. Mr. Brewster stressed the finding of the treasure and played down the details of Bortha's treachery. But that latter subject came up again, when Ramonez arrived from El Cielo, where he had left Bortha in the local jail.

It was Biff who asked the question that had been bothering him and Mike: "Tell us, Sefior Ramonez, how could Professor Bortha have been down under the excavation at the time of the cave-in, while he was dictating his notes on the machine up here?"

Ramonez raised his eyebrows. He turned to Mr.

THE FINAL RIDDLE 181.

Brewster. "This is the first I've heard about that. How long was Bortha dictating in his room?"

"About two hours," returned Mr. Brewster. "I was at the excavation with the boys. But Mrs. Brewster was here with the twins, and they heard Bortha dictating continually."

"Let's look at that machine."

In Bortha's room, Ramonez started the tape going, and they heard Bortha's voice, plainly recognizable, repeating the Toltec inscriptions and other data from his notes. After a few minutes, Ramonez stopped the machine and said: "Let's try the other tape."

"That's the only one that's been used," returned Biff.

"But you said that Bortha dictated for two hours," Ramonez reminded him, "and this is only an hour tape."

An idea was dawning on both Biff and Mike. But Ramonez, the experienced investigator, was just ahead of them.

"Allow ten to fifteen minutes from here up to the cavern," he estimated, looking from Bortha's window toward the back path leading to the pack trail. "Five minutes down the stairway in the cliff; five minutes coming up. Another ten to fifteen getting back here. How much is that, all told?"

"Thirty to forty minutes," replied Biff. "Which gave Bortha twenty minutes to chase away Chaco and the excavation workers, when he came there as Tizoc, and also to knock out those props that were all arranged to go. He could have done that job in fifteen minutes." Bortha turned to Mr. Brewster. "Or could he? As an expert, you would know."

"As an expert," smiled Mr. Brewster, "I would say that he could have done it in ten minutes-or even less."

Now, the boys exploded with what they had in mind.

"Then what Bortha did here," began Biff, "was dictate just for an hour, on one tape. Then he started the tape at the beginning and let it play back for another hour-"

"So they could hear his voice through the door," put in Mike, "as though his dictation was still going on. But all during that hour, he was playing the part of Tizoc-"

"And giving himself a perfect alibi," added Mr. Brewster. "There you have it, boys."

The last riddle of the Aztec treasure was solved.

THE END.

By ANDY ADAMS No. 4 in the Biff Brewster Mystery Adventure series