Thunder shook the unlit cavern as an immense, blue-white spark jumped between a pair of towering, metal columns. Instead of fading, the shimmering charge split in two and the twin streams of plasma began to circle their respective pillars. They moved like flames chasing the wind, racing around the columns and snaking their way upward toward the underside of a curved, metallic dome. There, they swirled together like the arms of a spiral galaxy, joining each other once again before vanishing in a final, eye-searing flash.

Darkness followed.

Ozone lingered in the air.

On the floor of the cavern, a group of men and women stood motionless, night-blind from the display. The flash had been impressive, but they’d all seen electricity before. Every one of them expected something more.

“Is that it?” a gruff voice asked.

The words came from Brigadier General Hal Cortland, a burly, squat figure of a man. They were directed at thirty-eight-year-old Daniel Watterson, a slight, blond-haired man wearing spectacles who stood by the controls of the great machine from which the artificial lightning had come.

Watterson studied a bank of dimly lit gauges. “I’m not actually sure,” he whispered to himself. No one had ever gotten this far, not even Michael Faraday or the great Nikola Tesla. But if Watterson was right — if his calculations and his theory and years of serving as Tesla’s apprentice had led him to understand what was about to occur — then the display of light they’d just witnessed should be only the beginning.

He switched off the main power, stepped away from the controls, and pulled the wire-rimmed glasses from his face. Despite the darkness, he could make out a soft blue glow coming from the columns. He raised his eyes to the dome above. An effervescent hue could be seen coursing around its inner surface.

“Well?” Cortland demanded.

Back at the console, one of the needles ticked up. Watterson saw it from the corner of his eye.

“No, General,” he said quietly, “I don’t think it’s quite finished.”

As Watterson spoke, a low rumble made its way through the cave. It sounded like heavy stones tumbling in some distant quarry, muffled and distorted, as if the vibration had to traverse miles of solid rock just to reach them. It rose for several seconds, then faded and ceased.

The general began to snicker. He switched on a flashlight. “Uncle Sam ain’t paying for a show with wet fireworks, son.”

Watterson didn’t reply. He was listening, feeling for something, for anything, at this point.

The general seemed to give up. “Come on, people,” he said, “the party’s over. Let’s get out of this mole hole.”

The group began to move. Their shuffling and mumbling made it impossible to hear.

Watterson raised a hand. “Please!” he called out loudly. “Everyone, stay where you are!”

The observers stopped in their tracks, and Watterson edged over to where the steel columns penetrated the rock floor. From there, they descended another five hundred feet “to get a firm grip on the Earth,” as Tesla once put it.

Laying a hand on one of the columns, Watterson felt a cold vibration. It surged through his body as if he’d become a part of the circuit. It wasn’t painful like electricity and didn’t make his muscles spasm, nor did it find its way to the ground and electrocute him. It was almost soothing, leaving him slightly dizzy, even a bit euphoric.

“It’s coming,” he whispered.

“What’s coming?” the general asked.

Watterson looked back. “The return.”

Cortland waited a few seconds before scowling. “You scientists are like barkers at a carnival: you think if you say something loud enough, and often enough, the rest of us will begin to believe it. But I don’t hear any—”

The general swallowed his words as the deep rumble made a second appearance. It surged through the cavern more emphatically this time, and the blue glow around the towers intensified, pulsing and matching the sound waves identically.

This time, when the waves faded, everyone held still. They were waiting for more. Forty seconds later they were rewarded. A third wave came through like a freight train passing by. It shook the cave underfoot and brought the swirl of lightning back to the polished surface of the dome above. The visible spiral of energy began descending the pillars, making it halfway down to the ground before vanishing.

Watterson pulled back, stepping away from the danger zone.

Moments later, a fourth reverberation surged into the cavern. The columns flared as it hit. Flashes of light jumped back and forth between them. The cavern began shaking. Dust and tiny bits of stone rained down from above, sending the witnesses scurrying for cover.

Watterson caught sight of General Cortland bathed in the light and grinning manically. Their roles had reversed. Now it was Cortland looking satisfied as Watterson began to worry. The scientist stepped toward the panel, slid his glasses back on, and studied the display. He couldn’t account for the vibration.

Before he could determine anything, a fifth wave hit. The vibration and the artificial lightning grew so intense, even the general seemed to realize something was wrong. “What’s happening?”

Watterson could barely hear him, but he was wondering the same thing. The power gauges — all but dead moments before — were heading toward their redlines.

A brief respite gave way to a sixth harmonic return, and the needles went off the scales. The shuddering was unbearable. Rocks were falling from above. A huge crack began to zigzag its way across the reinforced wall of the cave where the army had poured concrete to shore it up. Watterson had to grip the panel to stop from falling down.

“What’s happening?” the general repeated. Watterson wasn’t sure, but it couldn’t be good.

“Get everybody out of here,” he yelled. “Get them out — now!”

The general pointed toward the cagelike elevator that would take them four hundred feet to the surface. The group ran for it like a stampeding herd. But the tremors intensified and the far wall gave way before they could climb inside.

A thousand tons of rock and concrete plunged down on them. Those too close were crushed instantly. Others scrambled away just in time as the scaffolding-like frame of the elevator was bent and shoved aside.

Watterson began to panic. His hands flew back and forth across the controls, flicking switches and tapping gauges. The vibration was constant. The sound deafening.

Cortland grabbed him by the shoulder. “Turn it off!”

Watterson ignored him. He was trying to understand.

“Did you hear me?!” the general shouted. “Turn the damned thing off!”

“It is off!” Watterson shouted, pulling free of the general’s grasp.

“What?”

“It’s been off since after the first spark,” Watterson explained.

The latest wave faded, but on the panel he could see the next wave building. The needles went off the scale and Watterson’s face went white. Each wave had been bigger than the last. He feared to imagine what kind of power was on its way.

“Then where’s the energy coming from?” Cortland demanded.

“From everywhere,” Watterson said. “From all around us. That’s what the experiment was supposed to prove.”

The cavern began to shake once again. This time the lightning was not contained on the columns, it jumped around the room, flying into the walls, the ceiling, and the floor. Shards of stone and clouds of dust blasted out into the open space.

Amid the screams and panic, Watterson stood helpless, his moment of victory fading to utter catastrophe. From above him came the ominous sound of cracking.