Arthur Clarke - Cradle

It was time to submerge. Holding hands in the darkness, Nick and Troy dropped about five feet under the water. They stopped, equalized the pressure in their heads, and repeated the procedure. When they were down about ten feet, Troy turned on the searchlight. They quickly worked out their directions and headed around the corner, deeper into the cove adjoining Homer’s estate.

Troy was in the lead. He had no trouble finding the entrance to the natural tunnel that led to the subterranean cave. As they had planned, Nick waited outside the tunnel while Troy went inside to look for alarms. The rock cliffs closed over his head. The watery entryway was about five feet across and four feet high. Troy immediately found a metal box affixed to the left wall, where it was partially hidden from view. When he examined the box, he discovered that it was emitting two laser beams separated by about three feet.

On the other side of the natural tunnel were the receiving plates for the beams as well as the alarm electronics. Troy swam over carefully, pulled out his screwdriver, and dismantled the housing. The system was very simple. Failure of either plate to receive a beam would trigger the opening of a relay. When both relays were open, current could flow to the alarm. Thus an object had to be large enough to break both beams simultaneously to set off an alarm. Troy smiled to himself as he validated the operating principle by passing his hand in front of one of the beams. Then he jerryrigged one of the relays permanently closed. Satisfied with his work, he swam back and forth in the tunnel, breaking both beams at the same time, assuring himself that he had rendered the alarm system ineffective.

He swam back out to meet Nick and gave him the thumbs-up sign. The two men passed through the fifty yards of natural tunnel into the subterranean cave. Where the narrow passageway widened, Troy again gestured to Nick to remain behind while he, Troy, went into the cave to check for booby-traps. Nick let his feet fall to the bottom of the tunnel and switched on his own small flashlight. He was in a perfect place for an ambush. The tunnel was so small here that there was virtually no maneuvering room He wondered what an underwater sentry would look like. What a place to die, he thought suddenly. Fear swept over him as he turned off his flashlight and looked down at his illuminated diver’s watch. He watched the glowing second hand sweeping around the face. He tried to calm himself. It had been three minutes since Troy had left. Why is he taking so long? he asked himself. He must have found something. Another minute passed. Then another. Nick was having a hard time quelling the onset of panic. What do I do if he doesn’t return?

Just as Nick was about to swim into the cave on his own, he caught sight of Troy’s searchlight coming toward him Troy waved and Nick followed. Within thirty seconds they were in the shallow part of the cave, where the water was only about four feet deep. The two men stood up with their flippers lodged against the rocks to protect themselves from falling in the intermittent tidal surges.

Nick pulled his regulator out of his mouth and flipped his mask back on his head. Before he could speak, Troy put a finger against Nick’s lips. “Speak very softly,” Troy’s whisper was barely audible. “The place could be alarmed for sound as well.”

There was no light in the cave except Troy’s searchlight. However, over their heads, in the highest corners of the rock ceiling, Troy pointed out two separate banks of fluorescent lighting. The cave itself was an irregular oval, about thirty yards in its longest dimension and maybe fifteen yards across at its widest point. The ceiling was only about three feet above the water near the entrance to the tunnel out to the ocean, but it was twenty feet high in the corner where they were standing in the shallow water.

“Well, Professor,” Troy continued whispering, “I have good news and bad news. The bad news is that there is no treasure here in this cave. The good news is that there are two other tunnels, both manmade, that lead away from this place and go under Captain Homer’s property.” He paused for a moment and watched his partner. “Shall we go for it?”

Nick looked at his watch. It was nine-twenty already. He nodded. “The bastard spent a lot of money down here. They must have stolen more than I figured.” Nick adjusted his diving equipment.

“We’ll start with the tunnel on the left. As before, I’ll lead to look for trouble.” Troy cast his searchlight around on the ceiling. “This is a strange place. But beautiful. It looks like another planet, doesn’t it?”

Nick pulled his mask back over his face and slipped the regulator in his mouth. He flopped backward into the sea water. Troy followed and, once under the surface, showed Nick the way to the first manmade tunnel. This tunnel was on the other side of the cave, about twelve feet below the water at its lowest point. It was made of normal circular sewer pipe. The diameter of the pipe was about five feet, making the tunnel approximately the same size as the natural passageway between the ocean and the cave. Troy entered the tunnel gingerly. He swam back and forth from side to side, examining one wall for a few yards and then going across to the other. He almost missed the long, slender alarm box. It was embedded in the ceiling at a junction between two sections of sewer pipe and Troy just happened to look up before he triggered the alarm.

This system worked on a different principle. A camera or other optical device in the box on the ceiling took repeated images of a square foot of the tunnel bottom that was backlit by an illuminated square cleverly concealed below the normal concrete floor. Apparently some kind of data comparison algorithm in the alarm processor contained logic by which the consecutive pictures could be assessed, in terms of threat, and an alarm triggered if necessary. It was the most complicated device of its kind that Troy had ever seen and he quickly recognized the similarities between this system and the ocean telescope that had been onboard the Florida Queen. That means MOI designed and developed it, he thought to himself. So I’d best be careful. I bet the algorithm is set so that disturbances to the camera trigger the alarm as well.

Nick had swum over to the side of the tunnel, out of the way, and was watching Troy try to open up the alarm box without jiggling the optical instrument. To accommodate the almost two-inch width of the box, there was a gap of that size everywhere around the circle connecting the two sequential sections of pipe. Throughout the rest of the tunnel, all adjoining sections were cemented together. Here the passageway was discontinuous.

Curious, thought Nick. He idly shone his small flashlight into the blackness in the gap beside him, expecting to see nothing but a wall of rock. What in the world is that? he wondered, as his light fell upon some metal object that looked like a large grating. The grating was resting upon an old piece of railroad track. Nick looked more carefully. He could make out a gear box and some pulleys, but he had no idea how all these mechanical devices fit together.

Meanwhile Troy had managed to remove the housing from the alarm box without disturbing the camera and was busy trying to understand the inner workings of the system. Whew, he thought. This is much too complicated to figure out in five minutes. If I can just isolate the alarm, that should be enough. It was tough work under the water. But Troy was clever and the electronics were packaged in a logical fashion. He was able to find the alarm and disable it. Afterward Troy lingered for several seconds trying to determine the purpose of the other circuits connected to the alarm subassembly.

Nick had intended to show Troy what he had found in the gap; however, as he watched his friend struggling with the complex circuitry of the alarm box, he became again worried about the passage of time. It was now almost a quarter to ten. He caught Troy’s eye and pointed at his watch. Troy reluctantly abandoned his investigation of the alarm and proceeded down the tunnel.