"How did he find out about the 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 from the mainland from the north. The Harlem River isn't very wide at this point. Also, 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 to leave that section 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 here which separates it from the city, and the ruins of the bridges which connected with the mainland have been removed, so the animals can't get back across any more.
"Two years after he arrived, the Nipe was almost caught. He had managed, somehow—we're not sure yet exactly how—to get here from Asia. According to the psychologists who have been studying him, he apparently does not believe that human beings are any 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 island was searched, and the police were ready to start an inch-by-inch going over of the island two days later. But the Nipe 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 exhaustive analysis of the pattern of his raids had given us something to work with, that we decided that he must have found an opening into one of the tunnels up here in the game preserve." He gestured again at the map. "It wouldn't take him long to see that no human being had been down there in a long time. 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 edge of the island, where it stopped. "This tunnel goes underneath the Hudson River at this point, and emerges on the other side. It's only one of several that do so. They're all flooded now; the sun bomb caved them in when the primary shock wave hit the surface of the river.
"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 apparatus, he's practically a self-contained submarine. The pressure doesn't seem to bother him much. He's a tough cookie."