As one, Mulder and Scully dashed madly back into their car. Headlights sliced through the darkness as Mulder swung the car into a hard turn, and the engine roared as they took off after the train.

They followed it for a long time, the rails glowing faintly in the headlights as they arrowed straight into the night. Around them the countryside began to change, prairie gradu-ally giving way to higher ground, stone-covered hillocks and shallow canyons covered with dense underbrush. In the distance mountains loomed dead-black against a sky starting to fade to dawn. Foothills rose around them, choked with low-growing juniper and devil's-head cactus; except for the twin lines of the rails, there was no sign that any human had ever set foot here.

Then, very slowly, the tracks began to fol-low a long sloping upward grade. The belly of the rental car scraped against rocks, the wheels jounced in and out of foot-high ruts; and still they drove on, chugging uphill. Until, at last, they could go no farther; the railroad tracks dis-appeared into the mountain, with not the slightest hint of what might lie on the other side of the tunnel. The car swung across the rails, tires spinning on the gravel bed, and came to a stop at the edge of a gorge. Scully and Mulder clambered out, pulling on their jackets against the chill bite of desert air. In the near distance, beyond the gorge on the other side of the mountain, a strange opalescent glow stained the air.

"What do you think it is?" Scully asked in a low voice.

Mulder jammed his hands in his pockets and shook his head. "I have no idea."

They started toward it, stumbling as they climbed down the rough hillside. Before them a great plateau stretched as far as they could see, and at the edge of this rose what was illuminat-ing the night: two gigantic, glowing white domes that seemed to float in the darkness. Rolling to a stop beside them was the train that bore the unmarked tanker trucks.

Mulder pointed. Scully nodded, and with-out speaking they continued down, sliding through loose scree and grabbing onto dried shrubs to keep from falling. Finally they reached bottom. Ahead of them stretched the high desert plateau. They moved more quickly now, just short of running as they made their way across the waste. In the near distance something shimmered and rustled in the cold wind, and there was a grassy odor. But it wasn't until they were nearly upon it that the eerie glow from the domes revealed what lay before them.

" Look," breathed Scully in disbelief.

In the half light stretched acres and acres of cornfields, as incongruous in that desert as fresh water or snow-capped hills. Wind rippled through the stalks, corn tassels whispered; and Mulder and Scully walked slowly until they stood at the very edge of the field.

They entered the field, walking one behind the other down a row lined with stalks that grew two or three feet above their heads. Scully shook her head. "This is weird, Mulder."

"Very weird." He gazed to where the twin domes rose cloudlike above the distant edge of the field.

"Any thoughts on why anybody'd be grow-ing corn in the middle of the desert?"

Mulder flicked a fallen husk from his shoul-der and pointed at the domes. "Not unless those are giant Jiffy Pop poppers out there."

They went on, the wind rattling the stalks as they passed row after row of corn like some landscape in a nightmare; but at last they reached the far perimeter of the field. Together they stepped out into the open air.

In front of them, more vast than they could have imagined, were the two glowing domes. There was no evidence that anyone was guard-ing them. No vehicles, so sounds, no signs warning off trespassers.

For a moment the two agents stood staring at the eerie structures. Then they hurried cautiously toward the nearer of the two.

A heavy steel door served as entrance—no lock, no alarm system. Mulder pulled it, slowly and with some effort. It opened with a sucking sound, suggesting that the interior was pressur-ized. He shot Scully a curious look, then stepped inside, Scully at his heels.

Immediately they both jumped, crying out as large fans overhead sent blasts of air down onto them.

There was a thunderous roar, and they lunged ahead, into the echoing stillness of the space beyond.

"Cool in here," said Scully, shivering as she tugged at her jacket. She blinked; the dome was so painfully bright it was as though day-light reigned here, though she could see no lamps anywhere.

"Temperature's being regu-lated…"

"For the purpose of what!"

Mulder let his head fall back so that he was staring directly overhead. A dizzying web of cross wires and cables was strung there, giving an overall impression of simplicity and some perfect, unknown, function. When he looked down he saw a floor that was the earthbound counterpart to this high-wire act: gray and flat, of metal or some sort of sturdy resinous com-pound, and utterly featureless. All around them the air was still, but as the two agents moved cautiously through the dome, they gradually became aware of a sound. A steady, resonating hum—almost an electrical hum, but with a slightly different vibration that Mulder couldn't quite put a name to, as though the air channeled some energy that pulsed at a higher or lower frequency than was humanly recognizable.

They headed toward the middle of the vast open space, stepping with care on the gray sur-face underfoot, until they reached a dividing line where the floor gave way to the dome's epicenter, a space the size of a sports arena.

Before them, laid out in a grid and low to the ground, was row after row of what looked like boxes, sides touching as though they were pieces in some mammoth puzzle or game board. Each was about three feet square, with a dim pewter sheen. Mulder stepped very carefully onto one. It felt reassuringly solid, and after a moment Scully followed him, walking across the grid.

"I think we're on top of something, a large structure," Scully said when they paused to look around.

She stared down, frowning. It was apparent now that the boxes had louvered tops, but these were all firmly shut, so that whatever was inside could not be seen. She tapped gently at the box with her foot. "I think these are some kind of venting—"

Mulder stooped, to rest his head against the top of one box, listening. "You hear that?"

"I hear a humming. Like electricity. High voltage, maybe." She gazed overhead, at the bizarre Crosshatch of cables and struts and gird-ers spanning the interior of the dome.

"Maybe," said Mulder. "Maybe not."

Scully pointed skyward. "What do you think those are for?"

Above them, at the very top of the dome, were two huge louver vents corresponding to the smaller ones underfoot.

"I don't know," said Mulder, scrambling back up again.

They stood side by side, gazing at the ceil-ing when, without warning, a hollow metallic bang echoed through the dome.

In the dome's ceiling one of the vents was opening. As though some great invisible hand was there, the great metal louvers were strain-ing from their flat, closed position; until they pointed straight up and down. Open, so that Scully and Mulder could see a black slab of night beyond, and feel the chill air edging through the gap in the dome. When the first louver was completely open, the second began the same ominous performance, sliding until another series of apertures gaped onto the night. Mulder stared at it, mind racing as he tried to come up with some explanation for what was above them.

Cooling vents? But the dome was already chilly, the temperature maintained by some unseen refrigeration system. Brow furrowed, he looked down and around, searching for some-thing that might provide a clue. His gaze stopped when it came to the mysterious boxes underfoot.