Map of Bones (Sigma Force 2)

“So what do you want us to do?” Kat asked.

Gray settled to a stop. “We go back to square one. We’ve based our search on historical records available to anyone. The only advantage we have over all the treasure hunters of the past centuries is what was discovered under Saint Peter’s tomb. We missed a clue down there.”

Or one was stolen, Gray thought. But he did not speak this worry aloud.

“Maybe we didn’t miss a clue at the tomb,” Vigor said. “Maybe we didn’t look deep enough. Remember the catacombs. The riddles were multilayered, multifathomed. Could there be another layer to this riddle?”

Silence answered him…until an unexpected voice solved it all.

“That goddamn fiery star,” Monk swore. “It wasn’t just pointing down at the city of Alexandria…it was pointing down at the stone slab.”

Gray felt the ring of truth in Monk’s words. They had been so focused on the inscribed map, the fiery star, the implication of it all, but they had ignored the unusual medium of the artist.

“Hematite,” Kat said.

“What do you know about it?” Gray asked, trusting her background in geology.

“It’s an iron oxide. Large deposits have been found throughout Europe. It is mostly iron, but sometimes it contains a fair amount of iridium and titanium.”

“Iridium?” Rachel said. “Isn’t that one of the elements in the amalgam? In the Magi bones?”

“Yes,” Kat said, voice suddenly sounding strained over the radio. “But I don’t think that’s the significant part.”

“What?” Gray asked.

“I’m sorry, Commander. I should have thought of it. The iron in hematite is often weakly magnetic, not as strongly as magnetite, but it’s sometimes used as a lodestone.”

Gray realized the implication. Magnetism had also opened the first tomb. “So the star wasn’t just pointing to Alexandria, it was pointing to a magnetized stone, something we’re supposed to find.”

“And what did the ancient world do with lodestones?” Vigor asked, excitement growing in his voice.

Gray knew the answer. “They made compasses!” He fed air into his BC vest and rose toward the surface. “Everyone topside!”

11:10 A.M.

IN A matter of minutes, they were shedding tanks, vests, and weight belts. Rachel climbed into the pilot’s seat, glad to sit down. She pressed the button to raise the anchor. It chugged upward.

“Go slow,” Gray said. He had taken up a post at her shoulder.

“I second that,” Monk said.

“I’ll watch the compass,” Gray continued. “You keep us on a snail-paced circuit around the fort. Any twitch on the compass needle and we drop anchor and search below.”

Rachel nodded. She prayed that whatever magnetized stone lay down there, it was strong enough for their shipboard compass to detect.

With the anchor retracted, she eased the throttle to the barest chop of her propellers. Motion forward was barely detectable.

“Perfect,” Gray whispered.

Onward they glided. The sun slowly rose into the sky overhead. They pulled up the boat’s canopy to shade the group as the day’s heat climbed. Monk lay sprawled on the portside bench, slightly snoring. No one spoke.

Worry grew in Rachel with each slow turn of the boat’s propeller.

“What if the stone isn’t out here?” she whispered to Gray, who kept a vigil on the compass. “What if it’s inside the fort?”

“Then we’ll search there next,” Gray said, squinting toward the stone citadel. “But I think you’re right about a secret entrance. The hematite slab sat over a secret tunnel to the cavern that led down to a river channel. Water. Perhaps that’s another layer of the riddle.”

Kat heard them, a book open on her lap. “Or we’re reading too much into it,” she said. “Trying to force what we want to match the riddle.”

Up in the bow end, Vigor massaged a sore calf muscle from the swim. “I think the ultimate question of where the stone might lie—on land or in the water—depends on when the alchemists hid the clue. We estimated the clues were hidden sometime around the thirteenth century, maybe a little before or a little after, but that’s the critical era of conflict between Gnosticism and orthodoxy. So, did the alchemists hide their next clue before or after the Pharos Lighthouse collapsed in 1303?”

No one had an answer.

But a few minutes later, the compass needle gave a shaky twitch.

“Hold it!” Gray hissed.

The needle steadied again. Kat and Vigor glanced to them.

Gray placed a hand on Rachel’s shoulder. “Go back.”

Rachel tweaked the throttle into neutral. Forward momentum stopped. She let the waves bob them backward.

The needle pitched again, swinging a full quarter turn.

“Drop anchor,” Gray ordered.

She pressed the release, hardly breathing.

“Something’s down there,” Gray said.

Everyone began to move at once, grabbing for fresh tanks.

Monk woke with a start, sitting up. “What?” he asked blearily.

“Looks like you’re going on guard duty again,” Gray said. “Unless you want to take a dip?”

Monk scowled his answer.

Once the boat was secure and the orange flag raised, the same four divers fell back into the water.

Rachel bubbled out her buoyancy and sank under the waves.

Gray’s voice reached her through the radio. “Watch your wrist compasses. Zero in on the anomaly.”

Rachel studied her compass as she descended. The water was fairly shallow here. Less than ten meters. She reached the sandy bottom quickly. The others dropped around her, hovering like birds.

“Nothing’s here,” Kat said.

The seabed was a flat expanse of sand.

Rachel stared at her compass. She kicked a body length away, then back again. “The anomaly is right here.”

Gray lowered to the bottom and swept his wrist over the floor. “She’s right.”

He reached to his other wrist and unsheathed his knife. With the blade in hand, he began stabbing into the soft sand. The blade sank to the hilt each time. Silt stirred up, clouding the view.

On his seventh stab, the knife plainly jarred, failing to penetrate more than a few centimeters.

“Got something,” Gray said.

He sheathed the knife and began digging in the sand. The view grew quickly murky, and Rachel lost sight of him.

Then she heard him gasp.