And as the sun set and Cape Town found itself shut off from the world, the night of the second deadline began.

AT LENGTH, the Indian Raider came to the eastern coast of the Cape of Good Hope, a rugged peninsula of densely forested mountains and valleys.

Blasted all year round by biting winds from the Antarctic, and featuring many impa.s.sable gorges, it was an inhospitable place and even in the present day, uninhabited.

Nestled up against the immense bulk of Table Mountain on the other side of the peninsula was the modern city of Cape Town. Right now, two dozen South African Navy warships formed a semicircular perimeter around the city, covering the seaward approach.

Anch.o.r.ed in close to the rocky coastline about a mile south of the city's last seaside residence were a few unmarked American vessels and one private cruiser with Saudi Arabian markings that had arrived several days ago.

In a diving bell beneath those vessels, CIEF troops in scuba gear were busily at work, pulling a veil of seaweed from an ancient stone doorway cut into the rock wall of the coast.

It was the main entrance to the Second Vertex.

But as Jack knew, since the Second Vertex was modeled on the layout of the ancient city of Ur-or more correctly, Ur had been based on the mucholder Vertex-there was asecond entrance, one that arrived at it from the east before bending down to meet the vertex from the north.

"It's got to be around here somewhere," Lachlan said, eyeing the sub's GPS readout.

"I'm pinging the sh.o.r.e for voids and recesses," the Sea Ranger said. "But we have to be careful with the active sonar. If someone hears it, they'll know we're here."

He was firing sonar signals at the underwater sh.o.r.eline those signals then bounced back to theIndian Raider ...unless they disappeared inside an aperture in the rock wall.

"Sir!" a sonar operator called. "Sonar anomaly in the coastline, bearing 351. Depth 170 feet."

The Sea Ranger came over. So did Jack and the twins.

"Makes sense," Julius said. "Sea levels are a lot higher now than they would have been back then. An ancient entrance would be underwater now, like at the Cosquer Cave in southern France."

"Let's take a look," the Sea Ranger said. "Fire up the outside forward camera."

A monitor was switched on, showing the underwater world outside in ghostly nightvision green, thanks to a camera mounted on the sub's bow.

On the monitor, fish glided by, even a shark or two. Seaweed waved lazily in the current, and beyond it all, the rock wall of the coast cruised by- "There!" the Sea Ranger said abruptly, pointing at a blurry dark spot on the screen.

Jack leaned close, and his eyes widened.

"Sharpen focus," the Sea Ranger ordered.

The image was refined, came into clearer focus.

As it did, Jack knew they'd found it.

On the screen in front of him, partially covered by strings of twisting seaweed, was an ornate ancient doorway, huge in size, perfectly square in shape, and beautifully cut out of the solid rock around it.

"Holy s.h.i.t...we're here."

THE EASTERN ENTRANCE TO THE 2ND VERTEX.

TheIndian Raider jettisoned its trawler sh.e.l.l and dived.

Moving slowly, the sub pushed through the veil of waving seaweed that hung down over the ancient doorway and entered the darkness beyond it.

Twin beams of light lanced through the haze from the two floodlights mounted on its bow.

On the monitor inside the conning tower, Jack saw a square tunnel stretching away into darkness, boring into the very foundations of the Cape itself.

The Sea Ranger kept his men alert, kept them driving the sub slowly and carefully, now using his active sonar without restraint.

After about fifty minutes of this slow travel Jack saw something on the monitor that he'd seen before: columns.

Great, high stone pillars holding up a flat rockcut ceiling. And yet still the s.p.a.ce was wide enough for the 240 foot long submarine to fit between them.

"This place must be enormous..." the Sea Ranger whispered.

"You should have seen the last one," Jack said.

A wall of steps appeared in front of them. Just like at the First Vertex at Abu Simbel, it was an enormous mountain of steps,hundreds of them, all as wide as the pillared hall through which they were cruising. Only at this vertex, they went upward not downward, rising up and out of the water.

"Sir, I've spotted the surface," the sonarman said. "There's an opening up there, at the top of the steps."

"Let's see what's up there," the Sea Ranger said, swapping a look with Jack.

The Indian Raider rose gracefully through the spectacular underwater hall, gliding silently up past the hall's ma.s.sive pillars, following the incline of the submerged superstaircase.

Then it left the hall, breaking the surface.

TheIndian Raider 's conning tower rose silently out of a still body of water, seawater sliding off its sides.

It found itself hovering in a walled pool easily a hundred yards wide. It looked like a miniature harbor, foursided, with walls on two sides and the ultrawide stairs rising up out of the water on the third. On the fourth side, there were some stone buildings, half submerged.

Darkness filled the air above this miniharbor. But a sickly yellow light peeked over the horizon at the top of the steps, illuminating the s.p.a.ce.

It was a gargantuan cavern, the ceiling easily six hundred feet high.

The hatch on the conning tower swung open and the Sea Ranger and Jack emerged, gazing in wonder at the immense dark s.p.a.ce around their little sub.

Wickham drew a flare gun, but Jack stopped him.

"No! Wolf's already here."

He nodded up at the sickly yellow glow above them-the result of flares already fired elsewhere in the supercavern.

Within a few minutes, they'd rowed ash.o.r.e and, with the Sea Ranger and the twins beside him and Horus perched on his shoulder, Jack stepped up the wide hill of stairs, climbing them.

When they reached the top and beheld what lay beyond them, Jack let out a gasp of astonishment.

"G.o.d save us all," he whispered.

THE SECOND VERTEX.

AN UNDERGROUND city lay before him.

An entire city.

A collection of stone buildings, all of them tall and thin like towers, stretched away from him for at least five hundred yards. Bridges connected all of them-some dizzyingly high, others very low, others still were constructed of steeply angled stone stairways.

Ca.n.a.ls of water filled the "streets" between all these buildings, seawater that over the millennia had seeped in through the cave's two entrances and flooded the city's floor.

Dominating the forest of towers before him was a ma.s.sive ziggurat, a great stepped pyramid that rose up in the very center of the ghost city.

Exactly as it did in ancient Ur,Jack thought.

At the summit of this ziggurat was a very peculiar structure: an ultrahigh and very thin laddertype object that shot up vertically from the ziggurat's peak until it hit the rocky ceiling of the cavern two hundred feet above.

At the point where the ladder hit the cavern's ceiling, a series of runglike handholds led to the spectacular centerpiece of the cavern, a centerpiece that took Jack's breath away.

Looming off to the side of the underground city was another inverted pyramid-bronze and immense, exactly like the one Jack had seen at Abu Simbel.

It hung from the ceiling of this cavern, hovering like some kind of s.p.a.ceship above the vast indoor city, easily twice the size of the ziggurat below.

From where he stood, Jack couldn't see any buildings directly beneath the pyramid-he guessed that it hung suspended above a bottomless abyss like the one at Abu Simbel had done.

But unlike the one at Abu Simbel, this pyramid was surrounded by its supplicant city, an exact twin of the ancient Mesopotamian city of Ur.

Jack wondered if all six of the vertices were somehow subtly different, unique shrines built to complement a central upsidedown pyramid-Abu Simbel had a ma.s.sive viewing hall looking out at its pyramid this one had a city of spectacular bridges kneeling before it.

Suddenly, shouts and mechanical noises made Jack look up. They'd come from the other side of the cavern.

A flight of steep stone steps rose up the side of the nearest tower. Jack climbed them.

Arriving at the summit of the tower, he was rewarded with a full view of the immense cavern and a glimpse of exactly where he stood in this lifeordeath race.

Things didn't look good.

There, standing on a rooftop halfway across the vast cavern, having obviously got here some time ago, surrounded by the men of his quasiprivate army, was Wolf.

Jack swore.

His enemies were far more advanced across the labyrinth than he was. Once again he was starting from behind.

And then, among the group of soldiers standing immediately behind Wolf, Jack glimpsed a diminutive figure, and his heart sank.

He only saw the figure for a moment, but the image lodged in his brain instantly: head bowed, left arm in a sling, right hand gripping Jack's fireman's helmet, terrified and alone, it was a small black boy with gla.s.ses.

It was Alby.

COMPARATIVE POSITIONS OF JACK'S AND WOLF'S TEAMS THE CITY AND THE PYRAMID.

THE SECOND VERTEX.

BENEATH THE CAPE OF GOOD HOPE.

SOUTH AFRICA.

DECEMBER 17, 2007, 0255 HOURS.

JACK TOOK IN the monumental task ahead of him.

First he a.s.sessed Wolf's position, over on the other side of the cavern.

They must have entered via the main western harbor some time ago, because they were standing on a tower roughly halfway between their harbor and the ziggurat.

A big head start.

But as he looked more closely at them, Jack frowned. Wolf's troops seemed to be laying longbridging planks over the rooftop in front of them and then running across each plank to the next tower.

Jack then looked at his own situation and instantly he saw the reason behind their unusual method of travel.

The tower on which he stood hadno roof. In fact,all of the tower tops he saw from up here were roofless.

They were all completely hollow, like smokestacks.

And yet, curiously, nearly every rooftop was connected to two or three more rooftops by the dizzying network of bridges.

"Oh, man," Jack said, realizing. "It's a huge trap system."

Every roof that Jack could see from here was the same.

On each one there was a tonguelike platform stretching out from the leading edge of the roof to its middle, out over that tower's black hollow core.

Ringing this tonguelike platform were three smaller steppingstonelike platforms, each situated exactly halfway between the central platform and the roof's three other edges, and each requiring a substantial jump of about five feet to land on them.

Jack examined the rooftop on which he was standing.

Carved into the stone tongue on which he stood was some text written in the Word of Thoth. On each steppingstone was a similar carving.

"How does it work?" the Sea Ranger asked.

"Question and answer," Jack said. "This carving here, on the tongue, is the question. You jump on the steppingstone carved with the correct answer. If you're right, the stepping stone holds your weight."

"And if you're wrong?" Lachlan asked.

"If you're wrong, I imagine it doesn't hold your weight and you fall down the hollow of the tower."

The Sea Ranger looked down into the black void inside the tower before them. Its walls were sheer and slick. You'd never be able to climb out, if you hadn't already landed in something deadly.

Jack said, "I imagine the struts holding up the false steppingstones are made of a brittle material. They look strong, but they're not."

"But you have to getevery riddle right all the way across," Julius said. "Would you stake your life on your ability to answer all those riddles correctly?"