Free Subterranean by James Rollins

“Way to go, champ,” he whispered, but purposefully loud enough for Ashley to hear. “Now we both have dates.”
    Jason covered a smile with a small hand.
    Ashley rolled her eyes. Men.
    Lights out. From his window, Khalid watched the lamps wink out as the camp was put to bed, fake sunset in the darkened cave. The importance of circadian rhythms in a darkened environment had been explained earlier by Blakely. Peak performance required tuning the environment to a regular diurnal pattern of darkness and light.
    This worked well with his plans. Shadows wove a fine cloak.
    Soon only a scattering of bulbs were still lit. Except for the searchlight by the elevator. Its shaft of light stabbed the ceiling, circling in slow ovals around the stalactites, black fingers pointing down.
    He glanced at his watch. Ten o’clock. Time to go to work. He left his room and slipped out the dormitory’s entrance. The “night” was still warm, almost balmy, moisture thick in the air. Nothing like the dry nights at home. Desert sands remained hot well into the chilly night. Stars spread across the sky like the fires of Allah’s jihad.
    Passing through the residential half of the camp, winding among an acre of khaki tents, Khalid seldom strayed from the shadows. Yet he kept his gait casual in case any eyes spied him. On the far side of the camp, across a deep gorge, were the research labs and military headquarters. His destination, the elevator, was located within that distant encampment.
    His only obstacle: the bridge over the chasm. On the way from the elevator earlier today, he had noted it was guarded. That one guard was of no concern to him.
    Khalid continued across the sleeping camp. After edging around a final Quonset hut, he spied the bridge, made of wood and metal, lighted with lamps on the corners. One corner’s light had burned out. A single uniformed man leaned against a light pole, a rifle over his shoulder. A quick survey indicated the area was clear.
    Checking his pocket, Khalid stepped into the island of light by the bridge and strolled toward the black gorge. The guard took note of his approach, pushed off the post, and unslung his rifle. Khalid crossed to the chasm’s edge, a good yard from the bridge. Leaning over, he peered into the darkness, the chasm’s bottom remaining a black mystery.
    The guard, a young wheat-haired farm-boy type, called to him, “Careful, there. Those edges crumble away easily.”
    â€œI’ll be careful. Just wanted a look.” Khalid reached into his jacket’s breast pocket, noting the guard didn’t even raise an eyebrow at such a threatening move.
    Good.
    He pulled out a package of Winstons and tapped out a new cigarette. Popping it into his mouth, he returned the pack to his pocket and pulled a red Bic lighter out. He watched the guard from the corner of his eye as he lit up; the guard’s attention was transfixed by the flame.
    Khalid extinguished the lighter and dropped it into his side pocket, next to the knife. “Want a smoke?” he called over to the guard.
    The guard shrugged. “Thanks, man.” He left his post and crossed to where Khalid stood at the edge of the chasm.
    Khalid fished out his pack of cigarettes and shook a few out for the guard. “Take a couple.”
    The guard slipped one to his lips and another into his uniform pocket. “Got a light?”
    â€œSure.” Khalid reached into his pocket and wrapped his fingers around the stiletto, coughing to cover the click of the release as he pressed the button. “Have they ever searched the bottom of the chasm?”
    â€œNah.” The guard glanced at the black crevice. “Too damn deep.”
    â€œGood.” With the guard’s attention diverted, Khalid whipped out the knife and slashed deeply into the Marine’s neck, making sure to slice below the larynx to ensure a silent death. No scream, just a wet gurgle.
    Stepping back to