She sat up.

"What is it?" Ben asked, a concerned look on his face.

"Those amateurs said they had searched every square inch of this site. No artwork. No cave drawings." She pointed to the ceiling. "Then what the hell is that?"

Ben leaned over and twisted his head around. "What is what?"

"You have to lay down. I think that's why no one's found it." She moved to the side so he could lay down beside her. She pointed with the light of her headlamp. "Right there! Look!"

The crude carving stood in the circle of her light. Only a hand span wide, an oval was chiseled into the ceiling, bisected by a jagged line, like a lightning bolt.

Ben reached up and, with a long whistle, traced it with his finger. His next words were a whisper. "You know, this sort of looks familiar."

"What do you mean?" She expected some wisecrack.

"I've seen something like this. My granddaddy showed it to me."

"You're kidding."

"No, I'm serious." His voice sounded genuine. Almost amazed. "My great-grandmother was full Gagudja, an Aboriginal tribe in the Djuwarr region. Did I ever tell you that?"

"No."

He smiled an inch from her nose. "God's truth, my lady."

The man seemed to have more sides than the Pentagon. Either that or he was spinning a wild tale. She studied him and noted that his blue eyes were coldly serious. She swallowed and turned back to the design on the ceiling. "Does it remind you of anything specific?"

He shrugged, bumping her shoulder. "It's not exactly the same. But it looks sort of like the Gagudja symbol for one of their spirit peoples. One of their oldest, named Mimi."

She considered this information. Could there be some connection? Perhaps a lost Aboriginal tribe? But these dwellings were dated five million years ago. Aeons before the appearance of Aborigines on the Australian continent.

She frowned at the oval drawing. It was probably just a coincidence. She had seen the universality of some symbols across other cultures. Could this be the same case here? Hell, the symbol was rather basic. "This Mimi spirit," she began. "What type of spirit was it?"

"It's just nonsense. Stories."

"No, go on. Myths often have a kernel of truth. Tell me."

He patted the walls of the cave. "Mimis were spirits that lived in rocks."

She felt a chill crawl down her spine, noticing their stone enclosure.

"The Mimis taught the first Bushman to hunt and paint. They were greatly revered. And fear-"

Just then, Dr. Symski returned, standing at their feet. "What are you all doing?" His voice was both accusatory and embarrassed.

Conscious of their odd position, Ashley scrambled out. "I thought you searched this area."

"We did. Why?"

She pointed to the spot next to Ben. "Go look. Up on the roof."

The doctor crawled next to the Aussie. "My god!" he said when he looked where Ben pointed. "It's amazing. Jesus, what do you think it means?"

"I don't have a clue," she said, her hands on her hips, "but I mean to find out."

Linda, seated on a blanket, watched the crystal lake lap at the rocks along the shore a yard away. The water, clear as a window, teemed with small fish and other marine life. A luncheon basket, prepared by the mess hall cook, was open beside her. Two half-eaten sandwiches sat on a paper plate. Bologna and cheese.

"They look like little monsters," Jason said.

Smiling, Linda glanced over to the boy crouched over her portable Nikon microscope, viewing a water sample taken from the lake. "Those cone-shaped ones are called tintinnids," she said. "The squarish ones are diatoms."

"What are they? Some sort of bugs?"

"Not really. More like plants. They're in a family of organisms called phytoplankton. They take sunlight and convert it to energy the way a plant does."

"But if they need sunlight, like a plant"-Jason swiveled to face her, his face scrunched up with concentration-"how do they survive down here in the dark?"

She tousled his hair. "That's a very good question. I'm not really sure. But I believe there must be an underground current carrying the plankton from the surface waters to this underground lake. The water is very salty. Like diluted seawater."

"What's so important about… these…" He pointed at the microscope. "Bugs?"

As Linda considered the implication herself, she allowed her gaze to drift across the camp. She noticed a flurry of activity among the military personnel by the gorge that split the base. Probably some sort of training exercise.

"Well?" Jason asked, recalling her attention.

She turned back to the boy. "Do you want a science lesson?"

"Sure!" he replied enthusiastically.

"All right, you asked for it." She smiled at him, appreciating his inquisitiveness. "These plankton are the building blocks of life. On solid ground, grass turns sunlight into energy. Then a cow eats the grass. Then we eat the cow. This is the way the sun's energy is passed on to us. In the sea, it is the phytoplankton that turns sunlight into energy. The phytoplankton is then eaten by small creatures, such as jellyfish"-she pointed to the small fish just offshore-"which in turn get eaten by those tiny fish. Then even bigger fish eat the little fish. And so on. So even in the sea, sunlight's energy is passed along. Do you understand?"

"So these plankton thingies are like our grass."

"Exactly. They are the grassy fields from which this ecosystem sprouts."

He nodded. "Neat."

"So we've done step one and determined that the water is alive. Next, after we finish our sandwiches, we have to collect some of the creatures that live in the water. I saw some starfish close to the shore over there and some sponges. Wanna help me get a few?"

"You bet!"

"Later, one of the Marines promised to catch us one of those glowing fish too." She was curious about the phosphorescent properties of these large fish. Never having seen anything like them before, she grew excited by the prospect of classifying a new fish species.

"Why don't we start now?" Jason began to rise. "I saw some-"

"Hold it, young man." She pointed at the plate. "You finish your lunch first. You're my responsibility until your mother gets back."

He curled his lip and plopped back down on the blanket. "Oh, all right."

Passing him his sandwich, she took a bite of her own. "Let's hurry up, though. We've got fish to catch!"

"Big ones," he added with a small smile.

"The biggest. We could have them for dinner."

"Glowing fish? Yuck!"

"Hey, buddy, don't knock it. If the lights go out, you can still see what you're eating."

That started him laughing. She grinned, almost forgetting the miles of rock that hung over her head.

Ben watched Ashley bend over and study the altar site. Damn nice curves on that woman. He took off his helmet and wiped a red handkerchief across his damp forehead. It was getting late, and his stomach was growling. Thank god this was the last chamber to investigate.

He sighed as he watched Ashley pull out a measuring tape. "Not again," he cursed under his breath. Since this morning's discovery, he had felt like a third wheel, tagging along behind Ashley and Dr. Symski as they explored. Stopping in each chamber, measuring, scraping, sampling. Boring. He had hoped to spend more private time with Ashley, but with the discovery of the carving, both doctors were like bloodhounds on a scent. Nothing could distract them. Not a joke, not a quip. He was all but invisible.

"So this is where you found the diamond figurine?" Ashley knelt down beside the raised dais of stone. It mushroomed from the floor of one of the chambers. "The pedestal's carved from the base stone. Suggestive that the builders purposefully designed this chamber. All the other chambers have their firepits in this location." She pointed up to the ceiling. "Also this is the only room that doesn't have an oval symbol above the door."