"Perhaps not," Waverly said. "But if the original process is as slow as we suspect it to be from our discoveries at THRUSH test sites, there is the possibility we can prevent the entire Colorado River from crystallizing, thereby saving the fertile crop lands in Arizona and Southern California."

Illya realized then what Waverly meant. "Hoover Dam!"

"Precisely." Waverly said. "I'm going to put through a call immediately to the Secretary of the Interior at Washington and have his office instruct the personnel at Hoover Dam to close the locks. If that chemical hasn't reached the dam as yet, we can stop it before millions of dollars in damage can be wreaked."

"Do you want me to go to Pardee?" Illya asked. "THRUSH might still be in the area."

"I think not," Waverly said. "We'll let our people in Salt Lake City handle that. You'll fly directly to Hoover Dam."

Illya Kuryakin, with long pent-up emotions, was more than anxious to start. He was already on his way out the door.

FOUR

As he stood with his back braced against the wooden wall of the snow shed, looking down through the hole in the trestle floor at the hovering helicopter and the upraised machine gun, Napoleon Solo was struck with an intense, panic-tinged desire for self-preservation.

He knew he could not simply stand there like an immobile target in a shooting gallery. If nothing else, he had to male an effort, make a run for it, no matter how vain it may be. Solo moved just as the grinning THRUSH agent below him squeezed the trigger on the machine gun.

He leapt forward, across the crumbling ties, to the shed wall on the opposite side. He heard the chatter of the Thompson gun and saw a criss-cross of holes appear in the wall where he had been standing, showering splinters. Solo looked down through the hole. The front half of the propeller blades showed there; he was partially hidden from their view for the moment.

He looked through the length of the trestle. Not enough time there. There was only one way for him to go, and that was back the way he had come, back up the open trackbed. He tensed his body, staring down through the hole again. They were coming directly beneath him now. He could feel the wind from the spinning rotors. The noise of the helicopter filled the trestle, pounding against his ears.

Wait, he told himself. Wait until they're—

He saw it then. He saw it fully, for the first time, and his heart skipped a single beat. Hope all but dead inside him until then, surged, began to grow, replacing the resignation inside him, as an idea formed in his mind.

What Solo had seen was the long, steel section of rail that hung loosely on the side he was now standing on. The ties beneath it had been the ones that had given way, forming the hole in the bed, and the rail tilted downward slightly, touching empty space. It was still welded to the length of rail nearest him, but the welding was rusted and cracked nearly through.

He dropped to one knee, feeling the rotting ties beneath his feet give with a sharp creak. He reached out his right hand, grasping the rail lightly a few inches above the weld, and pressed downward, using the entire weight of his arm.

He heard the rusted metal rend, the sound loud, louder in his ears than the whirring helicopter below. The heavy rail dipped forward sharply. For a wild instant, Solo thought that it had snapped free completely. Not yet! his mind screamed. He threw himself prone, grabbing onto the rail with both hands, cupping them underneath.

The rail wobbled in his hands, still attached to the other by the thin piece of weld. Solo felt the pressure that the weight of the solid piece of steel exerted on his forearms, the tautness of the tendons and muscles there, and he knew he could not hold it for long. When that last connecting piece of weld snapped

Sweat rolled from his forehead into his eyes. His vision blurred. He leaned his head against one straining shoulder and rubbed the wetness away on the rough cloth of his shirt.

The helicopter was still maneuvring beneath him. He could see half of it now, the whirling, singing blades, part of the glass dome covering the cockpit, the huge, brown cargo body beneath it.

The helicopter sat motionless, half-in and half-out of Solo's view. His hands were white around the rail, and the pressure on his arms was unbearable. I can't hold it, he thought. I can't...

The chopper began to move. It dipped forward, banking under the trestle, under the hole in the track bed, and Solo saw the pilot then and in the next instant the man with the machine gun. The blades of the copter were tilted forward, directly beneath him now, and the body was raised out and to the side of the trestle wall.

The man with the machine gun saw him then. He saw Solo's head and arms extending out over the hole, and the grin contorted his face as it had before, and he raised the Thompson gun, leaning out of the helicopter doorway.

Solo let go of the rail. He felt the- release of pressure from his arms and heard the sharp crack as the last piece of steel snapped free.

The end of the rail nearest him jolted upward, narrowly missing Solo's chin, and then it plunged down through the hole.

There was just enough time for Solo to see the face of the man with the machine gun, to see the grin change into an expression of pure terror, and then the steel rail crashed with tremendous force into the rotating blades of the helicopter.

There was the grinding, tortured scream of twisted metal, the shattering sound of the glass dome breaking, and Solo saw one of the chopper blades, ripped in half, skim through the air and splinter against the granite canyon wall across from him.

The helicopter began to plunge. It dropped straight down at first, rotors crippled, and then it began to spin, a lazy, revolving spin, almost as if it were falling in slow motion. It grew smaller, smaller, trailing black smoke, a mere speck, and then it disappeared on the canyon floor below. It was quiet again.

Solo lay panting inside the trestle, head cradled in his arms at the edge of the hole. A fever-weakness seemed to have seized him. His chest heaved, and his arms felt slightly numb. He wanted to lay there, rest, just rest. Fatigue had seeped into every corner of his body.

But he got to his knees, and then, his fingers clawing at the rough shed wall, to his feet. He swallowed into a sore, parched throat. The helicopter would have radioed his position, Solo knew. THRUSH agents would be coming along the tracks after him at any moment. He still wasn't out of danger yet.

Solo stood hanging on to the shed wall. The only way past the hole, as he had seen before, was across that single steel rail. Legs rubbery, he stepped to the opposite side again. The ties beneath his feet did not seem any too sturdy. He knelt quickly there, testing the solidarity of the rail with his hand. It seemed firm enough to hold him.

Sweat drenched his entire body. He took a long breath, held it, and exhaled slowly. Then he stepped up onto the rail. It creaked, rocking faintly under him. Facing the shed wall, he leaned his body forward, both hands flat against the wood for balance, and to take his full weight from the rail.

He began to move his feet sideways, slowly, inching his way across the slippery piece of steel. He stared straight ahead, eyes on his hands as he slid them along the wall.

Splinters gouged into his skin, but he paid no attention to the stinging pain.

After what seemed like an eternity, he reached the other side of the hole. He paused there momentarily, breathing deeply, rubbing sheets of sweat from his face and eyes.

He walked through the trestle cautiously, watching the trackbed below him, bypassing ties and rails that looked to be rotted through or about to give way, stopping to test with his hands and feet areas that he was-not sure of. Finally, he reached the end of the trestle and stepped onto the solid ground of the tracks on the other canyon wall.