It was the ancient tri-spiral, the ubiquitous symbol found carved across the standing stones in England, illuminated in old Irish Celtic texts, and absorbed by the Catholic Church to represent the Holy Trinity.

The circle above, the spiral below.

And between them stood one object. It was the chamber's only feature.

"A Celtic Cross," Rachel said, her voice awed.

The others joined Gray as he entered the domed chamber.

The cross rose from the center of the tri-spiral. Sculpted also of bronze, it was plain, unadorned, only seven feet tall. It was constructed of two bronze poles crossed up high with a circular crosspiece.

Gray led the way.

Only Kowalski hung back by the tunnel. "I'll stay here," he said. "I remember what happened the last time you messed with a cross."

The four of them continued into the chamber.

Wallace commented on the simplicity of the religious sculpture. "Cistercian monks always preached against excessive adornment. They believed in austerity and minimalism. Everything in its place and serving its function."

Gray carefully crossed to the bronze spiral. He wasn't sure such a massive floor design could be classified as austere. But the professor was correct about the cross. In form and size, it seemed insignificant. In fact, it looked more like an industrial tool than a religious symbol.

Still, no one could deny its importance.

Rachel commented on it, looking up. "It stands between the spiral and the quartered cross."

Gray took a moment to shine his light across the dome. As his beam washed over the roof, he recognized something he'd missed. The dome, divided into four quarters, was not unadorned. His light reflected off raw chunks of quartz crystal imbedded in the ceiling.

As he cast his light around the dome, he knew what he was looking at.

"It's a starscape," Rachel said.

Gray agreed. He recognized constellations formed out of bits of quartz. The crystals varied in size, creating the illusion of three-dimensionality.

But they didn't have time to appreciate the artistry.

Seichan reminded them. "What about the key? Back at Bardsey Island, you thought the cross held the combination to unlock its vault. Could it be the same here? Look."

She pointed to the circular element hanging on the cross. The bronze wheel was scored with deep lines, similar to those on the stone cross on Bardsey.

Like the marks on a combination lock.

Gray suspected she was right, but there was a problem.

He didn't know the combination.

And the last time he'd tried, he'd almost gotten them all killed.

From everyone's worried expressions, they hadn't forgotten either.

"We have to attempt it," Wallace said.

"And if you trigger the booby trap," Seichan said, "we can have Kowalski yank that lever like last time."

He shook his head. "Even if it worked, we would still be screwed. Pulling the lever might haul our butts out of the fire here, but it could also reopen the stairs."

He eyed the others, letting the significance sink in. Commandos would flood down here.

"Out of the fire and into the bloody frying pan," Wallace concluded sourly.

Gray turned back to the cross. "We get one try. One mistake, and we're doomed."

Rachel offered the only solid reason for attempting it. "But we're just as doomed if we do nothing."

Kowalski added his own opinion. He grumbled it under his breath, but the acoustics carried it across the chamber.

"One more person says doomed and I'm out of here."

3:48 P.M.

Krista stood next to Khattab as the team's demolition expert finished packing the last hole with C-4 plastic explosive. He worked it with his fingers and shaped the charge with the deft skill of a sculptor. Once satisfied, he inserted a spark detonator tied to a wireless transmitter.

He waved everyone back.

They retreated out into the garden.

No one wanted to be under the walkway when it blew. The expert had warned that there was a chance the blast could collapse the walkway and bury the secret entrance.

"Ready?" Khattab asked.

She waved impatiently.

With a nod from Khattab, the demolitions expert lifted his transmitter and pushed the button.

3:49 P.M.

The blast dropped Rachel to one knee-not from any concussion, but from sheer fright. Already tense, she was caught off guard by the explosion. The meters of rock muffled the blast, but it still sounded like a gunshot.

"They're trying to blow their way inside," Seichan said, staring back at the tunnel.