“There’s nothing else on the paper?” Chase asked. “Hidden messages or anything?”

“What you see is what you get,” said Sophia. “Something as simple as invisible ink was the equivalent of quantum encryption in Plato’s time, so there’s nothing else to uncover. The clues must be in the words themselves.” She checked her watch. “Which you now have six minutes to find.”

Nina turned her attention back to the parchments, scanning through the text as quickly as she could. Words hidden within words… but which words? She read faster, the ancient, mottled ink almost becoming a blur as her eyes sped over each page.

But she knew she would find nothing that she hadn’t already discovered. If there was a cipher, its key was not contained within the text of Hermocrates. Either it was to be found in some other source not in her possession, in which case she had absolutely no chance of working it out…or there was no cipher.

“I know that face,” said Chase, for the first time in a while sounding hopeful.

Nina looked up at him. “Hmm?”

“That’s your crossword face, when you’ve just cracked a clue. What’ve you found?”

“Yes, what have you found?” said Sophia, taking a new interest. Corvus turned in his seat, watching Nina closely.

“I…I’m not sure yet. But I think I’ve been looking at the problem from the wrong angle. The reference to words being hidden within other words, I just assumed it was a cipher-specific individual words from the text combining to form a message.” She shuffled through the parchments to the first page. “But what if it’s not? The clue to finding the map on the back was quite literal-so maybe this is too. ‘The words of our friend Hermocrates reveal still other words within’…And ‘erubescent glass’…erubescent, red glass, colored glass…”

She looked up at the cabin roof. Above the front seats were windows in the ceiling, there to give the pilot a clear view of the rotor blades. They were tinted green to act as a sunscreen. Nina leaned forward and held out the page so the light of the sun overhead fell upon it. The entire page changed color to a garish emerald shade, the muddy tones of the ink becoming a darker brown.

Nina practically jumped from her seat. “I’ve got it, I’ve got it!”

“Got what?” Chase asked, confused.

“I need something red, red plastic or glass.” Nina looked around the cabin. “Come on, come on!” she snapped at Sophia. “Make yourself useful, find something!”

Sophia frowned, but did as she was asked. “Joe, hand me my bag. The blue one.” Komosa reached behind her seat, lifted out a traveling case and passed it to her. She searched through the contents. “Here,” she said, handing Nina a binder. “Will this do?”

“Perfect,” said Nina, snatching it from her. The binder contained pages bearing translations of Hermocrates from Greek to English, but she discarded them. The binder itself, with a cover of transparent red plastic, was what she wanted.

She placed the first sheet of parchment inside the binder, then held it by one of the windows, trying to get as much direct light onto it as possible. Beneath the plastic, the reddish-brown text almost vanished, its color absorbed by the red filter to leave nothing but a faint shadow.

But something else suddenly leaped from the page in perfect clarity.

Within the ghost words of the original text, individual letters stood out, what had previously seemed like discolored ink turning almost black…

“That’s what the line about seeing the world through erubescent glass meant,” Nina said, awed. “I thought the darker spots were just impurities in the ink-but they must have been added after the main text was written. Red glass was incredibly rare and valuable in Plato’s time, so very few people would have been able to find the hidden text. Somebody traced over the letters with a watered-down blue ink to hide a message, words within words. It could have been octopus ink, I suppose, or maybe-”

“They could have done it in ballpoint for all I care,” said Sophia impatiently. “What does it say?”

“Notebook, notebook.” Nina snapped her fingers. Chase couldn’t help but smile slightly at Sophia’s aggrieved expression as she passed Nina a notebook and pen. “Okay, let’s see…”

Somewhat awkwardly thanks to the handcuffs, she wrote down each highlighted letter in turn, a sentence in ancient Greek characters gradually taking form. “Well, that’s a promising start,” she said, translating it in her head. “It says the entrance faces the dawn.”

“Land by the eastern face of the mountain,” Corvus told the pilot. “What else?”

“I don’t know, that’s all I’ve got so far,” Nina told him testily. “I’ll need to keep working on it.”

“You’ll have to do it on the move,” Sophia said. “We’re here.”

Everyone looked ahead. Before them was a small rocky hill, a darker mound against the unending pale grays and browns of the dunes.

“That’s not exactly a mountain,” observed Chase, sounding let down. “It’s more like a zit. I thought Hercules would have something a bit more impressive.”

“Unlike some men, I doubt Hercules would feel any need to overcompensate,” said Sophia dryly. “Besides, I’m sure that the contents of the Tomb itself will be rather more impressive.”

The helicopter moved into a hover at the bottom of the hill’s eastern face, landing in a vortex of dust and grit. The other choppers followed it down.

“Spread out,” Corvus ordered over the radio. “There is an entrance somewhere-find it.” Armed men in desert camouflage jumped from the helicopters to begin the hunt. He turned back to Nina. “Dr. Wilde, keep working. I want as much information as possible about the interior of the Tomb by the time the entrance is located. Once it is found, I’m afraid you will have to work on the move.”

“Why the rush?” Chase asked. “It’s not like this is a race-nobody else even knows where the thing is.”

“I doubt that you would understand, Chase,” said Corvus, voice full of scorn. “You are a small man, with small and insignificant dreams. But when you have a dream like mine, and stand on the verge of seeing it become a reality… you too would not want to wait.”

“Hey, I have dreams that I want to see come true an’ all,” Chase told him. “Had one last night, in fact. You were in it. And so were you,” he added, nodding to Sophia, “and Joe Ring-Tits there.” He smiled coldly. “And I had a baseball bat. With nails in it.”

“Oh, do be quiet, Eddie,” Sophia huffed. She turned to Nina. “This is one of the reasons why I left him. He would never shut up. I’m sure you’ve noticed.”

“If everyone would shut up, I might be able to concentrate,” said Nina, annoyed.

With the power off, the temperature in the cabin rose quickly. Nina was the only one who didn’t notice, focused entirely on picking out the letters hidden among the text. She was on the ninth page of parchment when a call came in from one of Corvus’s men over the cabin speaker.

“Sir, this is Bertillon,” he said excitedly. “We found it, about two hundred yards to the north behind the tall rock.” Everyone looked to see a weather-worn stone pillar protruding from the hillside.

“Excellent,” said Corvus, stepping out of the cabin and donning a wide-brimmed sun hat. Komosa climbed through the rear door and held it open for Sophia, then dragged Chase from his seat and threw him onto the hot sand. Nina reluctantly followed, clutching the Hermocrates manuscript.

She squinted at the surrounding landscape, the glare of the sun against the ground dazzling her. Stinging sweat beaded around her eyes. Apart from the rolling dunes, which stretched to the horizon in every direction, the low hill was the only landmark to be seen.

The nearest town, Nina knew from the satellite images used at Corvus’s château to pinpoint the location of the Tomb, was almost a hundred miles away. Nobody came out here without a very good reason. While it was not the hottest desert on earth, the Grand Erg was still desolate and unforgiving.