"Well I'm damned," said Don. "How did you get here?" He did not bother to switch on the TV; he'd know Benj's signal anywhere. The porpoises must have been in the neighborhood and had spotted him before he'd even switched on the hunting call. For the thousandth time, he marveled at their intelligence and loyalty. It was strange that Nature had played the same trick twice —on land with the dog, in the ocean with the porpoise. Why were these graceful sea-beasts so fond of man, to whom they owed so little? It made one feel that the human race was worth something after all, if it could inspire such unselfish devotion.
It had been known for centuries that the porpoise was at least as intelligent as the dog, and could obey quite complex verbal commands. The experiment was still in progress, but if it succeeded then the ancient partnership between shepherd and sheep-dog would have a new lease on life.
Don switched on the speakers recessed into the sub's hull and began to talk to his escorts. Most of the sounds he uttered would have been meaningless to other human ears; they were the product of long research by the animal psychologists of the World Food Administration. He gave his orders twice to make sure that they were understood, then checked with the sonar screen to see that Benj and Susan were following astern as he had told them to.
The four echoes that had attracted his attention were clearer and closer now, and the main body of the whale pack had swept past him to the east. He had no fear of a collision; the great animals, even in their panic, could sense his presence as easily as he could detect theirs, and by similar means. Don wondered if he should switch on his beacon. They might recognize its sound pattern, and it would reassure them. But the still unknown enemy might recognize it too.
He closed for an interception, and hunched low over the screen as if to drag from it by sheer will power every scrap of information the scanner could give. There were two large echoes, some distance apart, and one was accompanied by a pair of smaller satellites. Don wondered if he was already too late. In his mind's eye, he could picture the death struggle taking place in the water less than a mile ahead. Those two fainter blips would be the enemy—either shark or grampus—worrying a whale while one of its companions stood by in helpless terror, with no weapons of defense except its mighty flukes.
Now he was almost close enough for vision. The TV camera in Sub 5's prow strained through the gloom, but at first could show nothing but the fog of plankton. Then a vast shadowy shape began to form in the center of the screen, with two smaller companions below it. Don was seeing, with the greater precision but hopelessly limited range of ordinary light, what the sonar scanners had already told him.
Almost at once he saw his mistake. The two satellites were calves, not sharks. It was the first time he had ever met a whale with twins; although multiple births were not unknown, a cow could suckle only two young at once and usually only the stronger would survive. He choked down his disappointment; this error had cost him many minutes and he must begin the search again.
Then came the frantic tattoo on the hull that meant danger. It wasn't easy to scare Benj, and Don shouted his reassurance as he swung Sub 5 round so that the camera could search the turgid waters. Automatically, he had turned toward the fourth blip on the sonar screen—the echo he had assumed, from its size, to be another adult whale. And he saw that, after all, he had come to the right place.
"Jesus!" he said softly. "I didn't know they came that big." He'd seen larger sharks before, but they had all been harmless vegetarians. This, he could tell at a glance, was a Greenland shark, the killer of the northern seas. It was supposed to grow up to thirty feet long, but this specimen was bigger than Sub 5. It was every inch of forty feet from snout to tail, and when he spotted it, it was already turning in toward the kill. Like the coward it was, it had launched its attack at one of the calves.
Don yelled to Benj and Susan, and saw them racing ahead into his field of vision. He wondered fleetingly why porpoises had such an overwhelming hatred of sharks; then he loosed his hands from the controls as the auto-pilot locked on to the target. Twisting and turning as agilely as any other sea-creature of its size, Sub 5 began to close in upon the shark, leaving Don free to concentrate on his armament.
The killer had been so intent upon his prey that Benj caught him completely unawares, ramming him just behind the left eye. It must have been a painful blow: an iron-hard snout, backed by a quarter-ton of muscle at fifty miles an hour is something not to be laughed at even by the largest fish. The shark jerked round in an impossibly tight curve, and Don was almost jolted out of his seat as the sub snapped on to a new course. If this kept up, he'd find it hard to use his String. But at least the killer was too busy now to bother about his intended victims.
Benj and Susan were worrying the giant like dogs snapping at the heels of an angry bear. They were too agile to be caught in those ferocious jaws, and Don marveled at the coordination with which they worked. When either had to surface for air, the other would hold off for a minute until the attack could be resumed in strength.
There was no evidence that the shark realized that a far more dangerous adversary was closing in upon it, and that the porpoises were merely a distraction. That suited Don very nicely; the next operation was going to be difficult unless he could hold a steady course for at least fifteen seconds. At a pinch he could use the tiny rocket torps to make a kill. If he'd been alone, and faced with a pack of sharks, he would certainly have done so. But it was messy, and there was a better way. He preferred the technique of the rapier to that of the hand-grenade.
Now he was only fifty feet away, and closing rapidly. There might never be a better chance. He punched the launching stud.
From beneath the belly of the sub, something that looked like a sting-ray hurtled forward. Don had checked the speed of his own craft; there was no need to come any closer now. The tiny, arrow-shaped hydrofoil, only a couple of feet across, could move far faster than his vessel and would close the gap in seconds. As it raced forward, it spun out the thin line of the control wire, like some underwater spider laying its thread. Along that wire passed the energy that powered the Sting, and the signals that steered it to its goal. Don had completely ignored his own larger craft in the effort of guiding this underwater missile. It responded to his touch so swiftly that he felt he was controlling some sensitive high-spirited steed.
The shark saw the danger less than a second before impact. The resemblance of the Sting to an ordinary ray confused it, as the designers had intended. Before the tiny brain could realize that no ray behaved like this, the missile had struck. The steel hypodermic, rammed forward by an exploding cartridge, drove through the shark's horny skin, and the great fish erupted in a frenzy of terror. Don backed rapidly away, for a blow from that tail would rattle him around like a pea in a can and might even cause damage to the sub. There was nothing more for him to do, except to speak into the microphone and call off his hounds.
The doomed killer was trying to arch its body so that it could snap at the poisoned dart. Don had now reeled the Sting back into its hiding place, pleased that be had been able to retrieve the missile undamaged. He watched without pity as the great fish succumbed to its paralysis.