The shark was a gigantic man-eater. It came straight for its prospective meal, not even circling to investigate. The mouth of the monster thing was open, revealing the horrible array of teeth.

The unfortunate sniper let out a weak, ghastly bleat. It seemed too late for anything to help the fellow. Renny, in discussing the affair later, maintained Doc purposely waited until the last minute so that terror would teach the sniper a lesson — show the man the fate of an evil-doer. If true, Doc's lesson was mightily effective.

With a tremendous spring, Doc shot outward and cleaved head-first into the water.

The dive was perfectly executed. And Doc, curving his powerful bronze body at the instant of impact with the water, seemed to hardly sink beneath the surface.

It looked like an impossible thing to do, but Doc was beside the unfortunate man even as the big shark shot in with a last burst of speed. Doc put himself between the shark's teeth and the sniper!

But the bronzed, powerful body was not there when the needled teeth slashed. Doc was alongside the shark. His left arm flipped with electric speed around the head of the thing, securing what a wrestler would call a strangle hold.

Doc's legs kicked powerfully. For a fractional moment he was able to lift the shark's head out of the water. In that interval his free right fist traveled a terrific arc — and found the one spot where his vast knowledge told him it was possible to stun the man-eater.

The shark became slack as a kayoed boxer.

Doc shoved the sniper ashore. The breed's swarthy face was a study. He looked like some one had jerked the cover off hell and let him see what awaited men of his ilk.

Now that the shark was atop the water, where rifle bullets could reach it, Renny and Monk put the finishing touch to the ugly monster.

"Why did you fire upon us?" Doc asked the breed, couching the words in Spanish. Doc spoke Spanish fluently, as he did many other tongues.

Almost eagerly, so grateful was he for what Doc had done, the breed made answer:

"I was hired to do it, senor. Hired by a man in Blanco Grande, the capital of Hidalgo. This man rushed me here during the night in a blue airplane."

"What was your employer's name?" Doc questioned.

"That I do not know, senor."

"Don't lie!"

"I am not lying to you, senor! Not after what you did for me a while ago. Truly, I do not know this man." The breed squirmed uneasily. "I have been a low mozo, hiring out for evil work to whoever pays me, and asking no questions. I shall desert that manner of living. I can take you to the spot where the blue airplane is hidden."

"Do that!" Doc directed.

They started off, reached the outskirts of town. Doc prepared to hail a fotingo, or dilapidated flivver taxi. Then he lifted his golden eyes to the heavens.

An airplane was droning in the hot copper sky. It came into view, a brilliant blue, single-motor monoplane.

"That is the plane of the man who hired me to shoot at you!" gasped the breed prisoner.

The gaudy blue craft whipped overhead, engine stacks bawling, and sped directly for the mud beach.

Without a word, Doc spun and ran with tremendous speed for the beach where Johnny, Long Tom, and Ham waited with his own plane.

Hslf-naked children gaped at the blur of bronze Doc made in passing them. And women muffled in rebozos, a combination shawl and scarf, scampered out and yanked them clear of the thundering charge of Renny and Monk and the prisoner, coming in Doc's wake.

On the beach a machine gun suddenly cackled. Doc knew by the particularly rapid rate of its fire that it was one he had brought along. His friends had set it up, were firing at the blue monoplane.

The blue plane dipped back of the tufted top of a royal palm, going down in a whistling dive. Then came a loud explosion. A bomb!

Up above the palm fronds the blue plane climbed. It was behaving erratically now. The pilot or some part of his azure ship was hit.

Straight inland it flew. And it did not come back.

Doc, reaching the beach, saw the bomb had been so badly aimed as to miss his plane fully fifty yards. His three men were sitting on the wing with the machine gun, grinning widely.

"We sure knocked the feathers off that bluebird!" Long Tom chuckled.

"He won't be back!" Ham decided, after squinting at the distant blue dot that was the receding aircraft. "Who was it?"

"Obviously one of the gang trying to prevent us reaching that land of mine in Hidalgo." Doc replied. "The member of the gang in New York radioed to Blanco Grande, the capital of Hidalgo that we were coming by plane. Right here is the logical place for us to refuel after a flight across the Caribbean. So they set a trap here. They hired this breed to machine-gun us, and when that didn't work, the pilot tried to bomb us."

At that moment Renny and Monk came up. They were both so big the breed looked like a little brown boy between them.

"What do we do with his nibs?" Monk asked, shaking the breed.

Doc replied without hesitation: "Free him."

The swarthy breed nearly broke down with gratitude. Tears stood in his eyes. He blubbered profuse thanks. And before he would depart, he came close to Doc and murmured an earnest question. The others could not hear the breed's words.

"What did he ask you?" Monk inquired after the breed had departed, with a strange new confidence in his walk.

"Believe it or not," Doc smiled, "he wanted to know how one went about entering a monastery. I think there is one chap who will walk the straight and narrow in the future."

"We better catch a shark and take him along if a close look at one reforms our enemies like that!" Monk laughed.

With ropes from a local warehouse, and long, thin palms which Doc hired willing natives to cut, the plane was snaked to dry land.

The news was bad. The floats were badly torn. They didn't have material for patching. Nor was there any in Belize. To save a great deal of work. Doc radioed to Miami for a fresh set. A transport plane brought the pontoons down.

Altogether, four days were lost before they got in shape for the air again.

NOT a morning did Doc miss his exercises. From his youth, he had not neglected the two-hour routine a single time. He did them, although he might have been on the go for many hours previously.

His muscular exercises were similar to ordinary setting-up movements, but infinitely harder, more violent. He took them without apparatus. For instance, be would make certain muscles attempt to lift his arm, while the other muscles strove to hold it down. That way he furthered not only muscular tissue, but control over individual muscles as well. Every part of his great, bronzed body he exercised in this manner.

From the case which held his equipment, Doc took a pad and pencil and wrote a number of several figures. Eyes closed, he extracted the square and cube root of this number in his head, carrying the figures to many decimal places. He multiplied and divided and subtracted the number with various figures. Next he did the same thing with a number of an even dozen figures. This disciplined him in concentration.

Out of the case came an apparatus which made sound waves of all tones, some of a wave length so short or so long as to be inaudible to the normal ear. For several minutes Doc strained to detect these waves inaudible to ordinary people. Years of this had enabled him to hear many of these customarily unheard sounds.

His eyes shut, Doc rapidly identified by the sense of smell several score of different odors, all very vague, each contained in a small vial racked in the case.

The full two hours Doc worked at these and other more intricate exercises.

The morning of the fifth day after arriving in Belize, they took the air for Blanco Grande, capital of Hidalgo.