Colonel Walther Mannheim tapped with one thick finger the map that glowed on the wall before him. "That's his nest," he said firmly. "Right there, where those tunnels come together."

Bart Stanton looked at the map of Manhattan Island and at the gleaming colored traceries that threaded their various ways across it. "Just what was the purpose of all those tunnels?" he asked.

"The majority of them were for rail transportation," said the colonel. "The island was hit by a sun bomb during the Holocaust and was almost completely leveled and slagged down. When the city was completely rebuilt afterwards, there was naturally no need for such things, so they were simply all sealed off and forgotten."

"He's hiding directly under Government City," Stanton said. "Incredible."

"It used to be one of the largest seaports in the world," Colonel Mannheim said, "and it very probably still would be if the inertia drive hadn't made air travel cheaper and easier than seagoing."

"How did he find out about those tunnels?" Stanton asked.

The colonel pointed at the north end of the island. "After the Holocaust, the first returnees to the island were wild animals which crossed over from the mainland to the north. The Harlem River isn't very wide at this point, as you can see. There was a bridge right at about this point here—the very tip of the island. It had collapsed into the water, but there was enough of it to allow animals to cross. Because of the rocky hills at this end of the island, there were places which were spared the direct effects of the bomb, and grasses and trees began growing there. That's why it was decided that section should be left as a game preserve when the Government built the capital on the southern part of the island." His finger moved down the map. "The upper three miles of the island, down to here, where it begins to widen, are all game preserve. There's a high wall at this point which separates it from the city, which keeps the animals penned in, and the ruins of the bridges which connected with the mainland have been removed, so animals can't get across any more.

"Two years after he arrived, the Nipe was almost caught. He had managed to get here from Asia by stealing a flyer in Leningrad. According to Dr. Yoritomo and the other psychologists who have been studying the Nipe, he apparently does not believe that human beings are anything more than trained animals. He was looking then—as he is apparently still looking—for the 'real' rulers of Earth. He expected to find them, of course, in Government City. Needless to say," said the colonel with a touch of irony, "he failed."

"But he was seen?" asked Stanton.

"He was seen. And pursued. But he got away easily, heading north. The whole island was searched, from the southern tip to the wall, and the police were ready to start an inch-by-inch combing of the game preserve by the end of the third day after he was seen. But he hit and robbed a chemical supply house in northern Pennsylvania, killing two men, so the search was called off.

"It wasn't until two years later, after an exhaustive analysis of the pattern of his raids had given us enough material to work with, that we determined that he must have found an opening into one of the tunnels up here in the game preserve." He gestured again at the map. "Very likely he immediately saw that no human being had been down there in a long time and that there wasn't much chance of a man coming down there in the foreseeable future. It was a perfect place for his base."

"How does he move in and out?" Stanton asked.

"This way." The colonel traced a finger down one of the red lines on the map, southward, until he came to a spot only a little over two miles from the southernmost tip of the island. The line turned abruptly toward the western shore of the island, where it stopped. "There are tunnels that go underneath the Hudson River at this point and emerge on the other side, over here, in New Jersey. The one he uses is only one of several, but it has one distinct advantage that the others do not. All of them are flooded now; the sun bomb caved them in when the primary shock wave hit the surface of the water. The tunnel he uses has a hole in it big enough for him to swim through.

"In spite of his high rate of metabolism, the Nipe can store a tremendous amount of oxygen in his body and can stay underwater for as long as half an hour without breathing apparatus, if he conserves his energy. When he's wearing his scuba mask, he's practically a self-contained submarine. The pressure doesn't seem to bother him much. He's a tough cookie."

"I'll remember that," said Stanton somberly. "I won't try to race him underwater."

"No," said Colonel Mannheim. "No, I wouldn't do that if I were you."

They both knew that there was a great deal more to it than that. In spite of the near miracle that the staff of the Neurophysical Institute had wrought upon Stanton's nerves and muscles and glands, they could only go so far. They could only improve the functioning of the equipment that Stanton already had; they could not add more.

His lungs could be, and had been, increased tremendously in efficiency of operation, but the amount of air they could actually hold could only be increased slightly. There was no way to add much extra volume to them without doing so at the expense of other organs. In a breath-holding contest, the Nipe would win easily, since his body had evolved organs for oxygen storage, while the human body had not.

You cannot make a silk purse out of a sow's ear if you are limited to the structures and compounds found in sows' ears. The best you can do is make a finer, stronger, more sensitive sow's ear.

"I understand that the Nipe has his hideout pretty well bugged with all kinds of alarms," Stanton said. "How did you get your own bugs in there without setting off his?"

"Well, at first we didn't know for sure what he was up to; we weren't even sure he was actually down in those tunnels. But we suspected that if he was he'd have alarms set all over the place—perhaps even alarms of types we couldn't recognize. But we had to take that chance. We had to watch him."

He walked over to the nearby table and opened a box some twelve inches long and five-by-five inches in cross-section.

"See this?" he said, as he took a furry object from the box.

It looked like a large rat. Dead, stiff, unmoving.

"Our spy," said Colonel Mannheim.

---

The rat moved along the rusted steel rail that ran the length of the huge tunnel. To a human being, the tunnel would have seemed to be in utter darkness, but the little eyes of the rat saw the surroundings as faintly luminescent, glowing from the infra-red radiations given out by the internal warmth of the cement and steel. The main source of the radiations was from above, where the heat of the sun and the warmth from the energy sources in the buildings on the surface seeped through the roof of the tunnel. But here and there were even brighter spots of warmth, spots that moved about on glowing feet and sniffed blindly at the air with tiny glowing noses. Rats.

On and on moved the rat, its little pinkish feet pattering almost silently on the oxidized metal surface of the rails. Its sensitive ears picked up the movements and the squeals of other rats, but it paid them no heed. Several times it met other rats on the rail, but most of them sensed the alienness of this rat and scuttled out of its way.

Once, it met a rat who did not give way. Hungry, perhaps, or perhaps merely yielding to the paranoid fury that was a normal component of the rattish mind, it squealed its defiance to the rat that was not a rat. It advanced, baring its rodent teeth in a yellow-daggered snarl of hate.

The rat that was not a rat became suddenly motionless, its sharp little nose pointed directly at the oncoming enemy. There came a noise, a tiny popping hiss, like that of a very small drop of water striking hot metal. From the left nostril of the not-rat, a tiny, glasslike needle snapped out at bullet speed. It struck the advancing rat in the center of the pink tongue that was visible in the open mouth. Then the not-rat scuttled backward faster than any real rat could have moved.

For a second the real rat hesitated, and it may be that the realization penetrated into its dim brain that rats did not fight this way. Then, as the tiny needle dissolved in its bloodstream, it closed its eyes and collapsed, rolling limply off the rail to the rotted wooden tie beneath.

The rat might come to before it was found and devoured by its fellows—or it might not. The not-rat moved on, not caring either way. The human intelligence that looked out from the eyes of the not-rat was only concerned with getting to the Nipe.

---

"That's how we found the Nipe," Colonel Mannheim said, "and that's how we keep tabs on him now. We have over seven hundred of these remote-control robots hidden in strategic spots throughout those tunnels now, and we can put more in whenever we want, but it took time to get everything set up this way. Now we can follow the Nipe wherever he goes, so long as he stays in those tunnels. If he went out through the one open-air exit up in the northern part of the island, we could have him followed by bird-robots. But"—he shrugged wryly—"I'm afraid the underwater problem still has us stumped. We can't get the carrier wave for the remote-control impulses to go very far underwater."

"How do you get your carrier wave underground to those tunnels?" Stanton asked. "And how do you keep the Nipe from picking up the radiation?"

The colonel grinned widely. "One of the boys dreamed up a real cute gimmick. Those old steel rails themselves act as antennas for the broadcaster, and the rat's tail is the pickup antenna. As long as the rat is crawling right on the rail, only a microscopic amount of power is needed for control, not enough for the Nipe to pick up with his instruments. Each rat carries its own battery for motive power, and there are old copper power cables down there that we can send direct current through to recharge the batteries. And, when we need them, the copper cables can be used as antennas. It took us quite a while to work the system out, but it's running smoothly now."

Stanton rubbed his head thoughtfully. Damn these gaps in my memory! he thought. It was sometimes embarrassing to ask questions that any schoolboy should know the answers to.

"Aren't there ways of detecting objects underwater?" he asked after a moment.

"Yes," said the colonel, "several of them. But they all require beamed energy of some kind to be reflected from the object we want to look at, and we don't dare use anything like that." He sat down on one corner of the table, his bright blue eyes looking up at Stanton.

"That's been our big problem all along," he said seriously. "We have to keep the Nipe from knowing he's being watched. In the tunnels themselves, we've only used equipment that was already there, adding only what we absolutely had to—small things. A few strands of wire, a tiny relay, things that can be hidden in out-of-the-way places and can be made to look as though they were a part of the original old equipment. After all, he has his own alarm system in that maze of tunnels, and we have deliberately kept away from his detecting devices. He knows about the rats and ignores them. They're part of the environment. But we don't dare use anything that would tip him off to our knowledge of his whereabouts. One slip like that, and hundreds of human beings will have died in vain."

"And if he stays down there too long," Stanton said levelly, "millions more may die."

The colonel's face was grim as he looked directly into Stanton's eyes. "That's why you have to know your job down to the most minute detail when the time comes to act. The whole success of the plan will depend on you and you alone."

Stanton's eyes didn't avoid the colonel's. That's not true, he thought, I'll be only one man on a team. And you know that, Colonel Mannheim. But you'd like to shove all the responsibility off onto someone else—someone stronger. You've finally met someone that you consider your superior in that way, and you want to unload. I wish I felt as confident as you do ... but I don't.

Aloud, he said: "Sure. Nothing to it. All I have to do is take into account everything that's known about the Nipe and make allowances for everything that's not known." Then he smiled. "Not," he added, "that I can think of any other way to go about it."

---