“Half a mile,” Painter said.

Looks of relief spread among the others.

But Coral stepped to his side, noting his tension.

“Cassandra’s already here,” he said. “Off to the east.”

Coral shrugged. “That’s good. When the sandstorm hits, she’ll be pinned down. It might buy us another day or two out here. Especially if that coastal high-pressure system crashes on top of us. The predicted megastorm.”

Painter nodded, taking a deep breath. Coral was right. They could still pull this off. “Thanks,” he mumbled to her.

“Anytime, Commander.”

They quickly divided the gear. The largest crate held the ground-penetrating radar unit. Painter and Omaha hauled it between them. It was monstrously heavy, but if they were to search the ruins for buried treasure, they might need such a tool.

So they set off, winding around a vast dune that crested two football fields in height, then slogged up and over smaller ones. The sun continued its climb, heating the sand and the air. Soon their pace became a crawl as they were drained of adrenaline, bone-tired and exhausted.

But at last, they climbed a low dune and discovered a cluster of modern cinder-block buildings, wooden structures, and a small mosque in the valley beyond. The village of Shisur.

Down in the valley, the endless red of the Rub‘ al-Khali was interrupted by green. Acacia bushes grew alongside the buildings, stretches of yellow-flowering tribulus spread across the sand, along with thickets of palmetto. Larger mimosalike trees trailed flowering fronds to the ground, creating shaded arbors. And the ubiquitous date palms climbed high.

After the desert trek, where the only vegetation had been a few straggly salt bushes and wan patches of tasseled sedge, the oasis of Shisur was Eden.

In the village, nothing moved. It appeared deserted. The winds had kicked up again as the forward edge of the storm pushed toward them. Bits of refuse spun in dust devils. Cloth curtains flapped out open windows.

“No one’s here,” Clay noted.

Omaha stepped forward, scanning the tiny township. “Evacuated. Then again, the place is pretty much abandoned during the off-season. Shisur is mostly a waystation for the wandering Bait Musan tribe of Bedouin. They come and go all the time. With the discovery of the ruins just outside the town and the beginning of tourism here, it has grown into a somewhat more permanent village. But even that’s pretty seasonal.”

“So where exactly are the ruins?” Painter asked.

Omaha pointed off to the north. A small tower of crumbling rock poked above the flat sands.

Painter had thought it a natural outcropping of limestone, one of the many flat-topped mesas that dotted the desert. Only now he noted the stacked stones that composed the structure. It look like some watchtower.

“The Citadel of Ubar,” Omaha said. “Its highest point. More of the ruins are hidden below, out of sight.” He set off toward the empty township.

The others began the final push to shelter, leaning against the stubborn wind, faces turned from the gusts of sand.

Painter remained a moment longer. They’d made it to Ubar at last. But what would they find? He stared at the danger looming to the north. The sandstorm filled the horizon, erasing the rest of the world. Even as he stared, Painter watched more of the desert being eaten away.

Again crackles of static electricity danced where the storm met the sands. He watched a particularly large discharge roll down a dune face, like a balloon cast before a stiff wind. It faded in moments, seeming to seep into the sand itself and vanish. Painter held his breath. He knew what he had just witnessed.

Ball lightning.

The same as had ignited the meteorite at the British Museum.

They had come full circle.

A voice spoke at his shoulder, startling him. “The blue djinn of the sands,” Barak said, having noted the same natural phenomenon. “Storms always bring out the djinn.”

Painter glanced to Barak, wondering if the man believed they were evil spirits or just a story to explain such phenomena.

Barak seemed to sense his question. “Whatever they are, they’re never good.” He set off down the hill after the others.

For a moment longer, Painter studied the monstrous storm, eyes stinging from the blowing sand. It was just beginning.

As he headed down the slope, his gaze cast off to the east. Nothing moved. The roll of dunes hid everything. A vast sea. But Cassandra and her team waited out there.

Sharks…circling and circling…

8:02 A.M.

S AFIA HAD not expected this mode of transportation, not from an ancient clan whose bloodline ran back to the Queen of Sheba. The dune buggy ramped up the sandy face, its huge knobby tires finding good traction. They shot over the crest, flew airborne for an extended breath, then landed solidly on the downward slope. Tires and shock absorbers cushioned their impact.

Still, Safia clung with her one good arm to the roll bar in front of her, like the security latch on a roller-coaster car. Kara held fast in the same manner, white-knuckled. Both women wore matching desert cloaks, hoods pulled up and secured with a sand scarf over their lower face, protecting skin from the scouring wind. They also wore polarized sun goggles, pinched over their eyes.

In the passenger seat up front, Lu’lu rode next to the Rahim driver, a young woman of sixteen named Jehd. The driver—or pilot, as the case was at times—held her lips in a firm, determined line, though a glint of girlish excitement lit her eyes.

Other dune buggies followed, each loaded with five of the clan women. They crisscrossed one another’s paths to avoid the sand cast up by the vehicles in front. To either side, flanking the buggies, rode a dozen sand bikes, motorcycles with ballooned wheels, chewing through the larger vehicles’ wakes, making huge leaps over the crests of dunes.

The caravan’s speed was born of necessity.

To the north, the sandstorm barreled toward them.

Upon leaving the subterranean warren of tunnels, Safia found herself on the far side of the Dhofar Mountains, at the edge of the Rub‘ al-Khali. They had crossed under the entire mountain range. The passages they had traversed were old river channels, worn through the limestone bedrock.

Free of the tunnels, the buggies and bikes awaited them. Kara had commented on the choice of vehicles, expecting camels or some other less sophisticated means of transportation. Lu’lu had explained: We may trace our lineage into the past, but we live in the present. The Rahim did not live their entire lives in the desert, but like the Queen of Sheba herself, they wandered, educated themselves, prospered even. They had bank accounts, stock portfolios, real-estate holdings, traded in oil futures.

The group now raced toward Shisur, trying to beat the storm.

Safia had not argued against such haste. She did not know how much longer the ruse she had used to deceive Cassandra would last. If they were to gain the prize before Cassandra did, they would need every advantage.

Lu’lu and the others were counting on Safia to lead the way. In the hodja’s words: The keys revealed themselves to you. So will the Gates. Safia prayed the woman was right. She had used intuition and knowledge to lead them this far. She hoped her expertise would carry her the rest of the way.

In the front seat, Lu’lu lifted a Motorola walkie-talkie and listened, then spoke into it. All words were lost to the growl of motors and torrents of winds. Once done, she swung around in her seat-belt restraints.

“There may be trouble,” Lu’lu yelled. “The scouts we sent ahead report a small band of armed strangers entering Shisur.”

Safia’s heart leaped to her throat. Cassandra…

“Perhaps they are just seeking shelter. The scouts found a vehicle. An old van stuck in a camel wallow.”

Kara leaned forward, intense. “A van…was it a blue Volkswagen?”

“Why?”

“It may be our friends. Those who were helping us.”

Kara glanced to Safia, eyes hopeful.

Lu’lu lifted her walkie-talkie and carried on a brief conversation. She nodded, then turned to Kara and Safia. “It was a blue Eurovan.”

“That’s them,” Kara exclaimed. “How did they know where to find us?”

Safia shook her head. It seemed impossible. “We should still be careful. Maybe Cassandra or her men captured them.”

And even if it was their friends, a new fear clutched Safia’s heart. Who had survived? Painter had attempted to rescue her, risked all, stayed behind to cover her retreat. Had he made it out? The exchange of gunfire she had heard as she fled the tomb echoed in her head.

All answers lay at Shisur.

After another ten minutes of dune racing, the small township of Shisur appeared over a ridge, in a slight valley, surrounded by the rolling desert. The village’s tiny mosque poked its minaret above the tumble of shacks and cinder-block buildings. The buggies all stopped below the ridgeline. A few of the women climbed out and up to the sandy crests. They dropped flat, their cloaks matching the sands, clutching sniper rifles.

Fearing a volley of accidental gunfire, Safia exited the buggy. Kara followed. She crossed up to the ridge. Caution drew her to hands and knees.

Across the village, she saw no sign of movement. Had they heard the approach of the dune buggies and gone into hiding, fearing the unknown group?

Safia surveyed the area.

To the north, ruins covered fifteen acres, surrounded by crumbling walls, excavated from the sands and reconstructed. Guard towers interrupted the walls at regular intervals, roofless stony circles, a story high. But the most dramatic feature of the ruins was its central citadel, a three-story structure of stacked stone. The castle perched atop a low hill that overlooked a deep ragged cleft in the ground. The hole encompassed most of the land within the walls. Its bottom lay in shadows.

Safia knew that the ruins of the hilltop fortress were only half of the original structure. The other half lay at the bottom of the hole. Destroyed when the sinkhole opened up under it, taking down sections of walls and half the castle. The tragedy was explained by the continual drop of the land’s water table. A natural limestone cistern lay underneath the city. As the water inside it dropped from drought and overuse, it left behind a hollow subterranean cavern that eventually collapsed in on itself, taking out half the city.