Five minutes later, he was still waiting on hold, when Stern walked into the room, shaking his head. "You're not going to believe this."

"Yes? What?" Marek said, holding the phone.

Stern just handed him a sheet of paper. It said:

"What is this supposed to be?" Marek said.

"The date on the ink."

"What are you talking about?"

"The ink on that parchment," Stern said. "It's six hundred and thirty-eight years old, plus or minus forty-seven years."

"What?" Marek said.

"That's right. The ink has a date of A.D. 1361."

"What?"

"I know, I know," Stern said. "But we ran the test three times. There's no question about it. If the Professor really wrote that, he wrote it six hundred years ago." Marek flipped the paper over. On the other side, it said:

AD 1361 ± 47 years

On the phone, the music ended with a click, and a taut voice said, "This is Bob Doniger. Mr. Marek?"

"Yes," Marek said.

"You may not remember, but we met a couple of years ago, when I visited the site."

"I remember very well," Marek said.

"I'm calling about Professor Johnston. We are very concerned for his safety."

"Is he missing?"

"No, he's not. We know exactly where he is."

Something in his tone sent a shiver down Marek's spine. Marek said, "Then can I speak to him?"

"Not at the moment, I'm afraid."

"Is the Professor in danger?"

"It's difficult to say. I hope not. But we're going to need the help of you and your group. I've already sent the plane to get you."

Marek said, "Mr. Doniger, we seem to have a message from Professor Johnston that is six hundred years-"

"Not on a cell phone," Doniger said, cutting him off. But Marek noticed that he didn't seem at all surprised. "It's three o'clock now in France, is that right?"

"Just after, yes."

"All right," Doniger said. "Pick the three members of your team who know the Dordogne region best. Drive to the airport at Bergerac. Don't bother to pack. We'll supply everything when you get here. The plane lands at six p.m. your time, and will bring you back to New Mexico. Is that clear?"

"Yes, but-"

"I'll see you then."

And Doniger hung up.

David Stern looked at Marek. "What was that all about?" he said.

Marek said, "Go get your passport."

"What?"

"Go get your passport. Then come back with the car."

"We going somewhere?"

"Yes, we are," Marek said.

And he reached for his radio.

Kate Erickson looked down from the ramparts of La Roque Castle into the inner bailey, the broad grassy center of the castle, twenty feet below. The grass was swarming with tourists of a dozen nationalities, all in bright clothes and shorts. Cameras clicking in every direction.

Beneath her, she heard a young girl say, "Another castle. Why do we have to go to all these stupid castles, Mom?”

The mother said, "Because Daddy is interested."

"But they're all the same, Mom."

"I know, dear…"

The father, a short distance away, was standing inside low walls that outlined a former room. "And this," he announced to his family, "was the great hall."

Looking down, Kate saw at once that it wasn't. The man was standing inside the remains of the kitchen. It was obvious from the three ovens still visible in the wall to the left. And the stone sluice that had brought water could be seen just behind the man as he spoke.

"What happened in the great hall?" his daughter asked.

"This is where they held their banquets, and where visiting knights paid homage to the king."

Kate sighed. There was no evidence a king had ever been to La Roque. On the contrary, documents indicated that it had always been a private castle, built in the eleventh century by someone named Armand de Clery, and later heavily rebuilt early in the fourteenth century, with another ring of outer walls, and additional drawbridges. That added work was done by a knight named Francois le Gros, or Francis the Fat, around 1302.

Despite his name, Francois was an English knight, and he built La Roque in the new English style of castles, established by Edward I. The Edwardian castles were large, with spacious inner courtyards and pleasant quarters for the lord. This suited Francois, who by all accounts had an artistic temperament, a lazy disposition, and a propensity for money troubles. Francois was forced to mortgage his castle, and later to sell it outright. During the Hundred Years War, La Roque was controlled by a succession of knights. But the fortifications held: the castle was never captured in battle, only in commercial transactions.

As for the great hall, she saw it was off to the left, badly ruined, but clearly indicating the outlines of a much larger room, almost a hundred feet long. The monumental fireplace - nine feet high and twelve feet wide - was still visible. Kate knew that any great hall of this size would have had stone walls and a timber roof. And yes, as she looked, she saw notches in the stone high up, to hold the big horizontal timbers. Then there would have been cross-bracing above that, to support the roof.

A British tour group squeezed past her on the narrow ramparts. She heard the guide say, "These ramparts were built by Sir Francis the Bad in 1363. Francis was a thoroughly nasty piece of work. He liked to torture men and women, and even children, in his vast dungeons. Now if you look to the left, you will see Lover's Leap, where Madame de Renaud fell to her death in 1292, disgraced because she was pregnant by her husband's stable boy. But it is disputed whether she fell or was pushed by her outraged spouse…"

Kate sighed. Where did they come up with this stuff? She turned to her sketchbook notes, where she was recording the outlines of the walls. This castle, too, had its secret passages. But Francis the Fat was a skilled architect. His passages were mostly for defense. One passage ran from the ramparts down behind the far wall of the great hall, past the rear of the fireplace. Another passage followed the battlements on the south ramparts.

But the most important passage still eluded her. According to the fourteenth-century writer Froissart, the castle of La Roque had never been taken by siege because its attackers could never find the secret passage that permitted food and water to be brought to the castle. It was rumored that this secret passage was linked to the network of caves in the limestone rock below the castle; also that it ran some distance, ending in a concealed opening in the cliffs.

Somewhere.

The easiest way to find it now would be to locate where it ended inside the castle and to follow it back. But to find that opening, she would need technical help. Probably the best thing would be ground radar. But to do that, she'd need the castle empty. It was closed on Mondays; they might do it next Monday, if-

Her radio crackled. "Kate?"

It was Marek.

She held the radio to her face, pressed the button. "Yes, this is Kate."

"Come back to the farmhouse now. It's an emergency."

And he clicked off.

Nine feet underwater, Chris Hughes heard the gurgling hiss of his regulator as he adjusted the tether that held him in place against the current of the Dordogne. The water clarity was not bad today, about twelve feet, and he was able to see the entire large pylon of the fortified mill bridge, at the water's edge. The pylon ended in a jumble of large cut rocks that ran in a straight line across the river. These rocks were the remains of the former bridge span.

Chris moved along this line, examining the rocks slowly. He was looking for grooves or notches that would help him determine where timbers had been used. From time to time, he tried to turn one rock over, but it was very difficult underwater because he could get no leverage.