It was not icy beneath the earth. Not shivering cold. It was more like the chill of death, when what was alive becomes empty of spirit. But nothing here had ever been touched by life. The rocks, never covered with seeds and flowers. The pools of water, never drunk from. The air, never drawn into lungs. All was devoid of meaning, as if it were a book written in nonsense syllables.

I have risked everything on this throw of the dice. If I am right, I will save Guillaume. If I am wrong . . .

If I am wrong, I will be near him when he goes to die.

Poulet faced resolutely ahead. “I’ll bring you as close as I can. The maps of the quarries are a wish and a guess, mostly. The maps of the streets of Paris aren’t reliable. Matching one to the other . . .”

He wishes to tell me we may fail. I already know that.

She cupped her hand near the candle for the comfort of it. To hold on to the light. “My father spent an entire winter, six years ago, measuring distances in Paris. He went with a gang of three men and lengths of chain. He was famous for a time.” She had been briefly, humiliatingly notorious as his daughter. “Then he dropped heavy weights off of high buildings with great exactitude. Gravity is stronger near water, he thinks. Or weaker. I never got it straight.”

“I know he is your father, but—”

“He is mad. There is no one who knows it better than I do. But he is an accurate madman. Madness will not keep him from finding the Convent of Saint-Barthélémy for me.”

Papa had come to the end of his discussion of magnetism and paused to consult the plaque on the wall. Justine obligingly held a candle for him.

87 G 1777.

The numbers were cut into stone on the wall at this corner, cut deep, and then each line fixed in emphatic black. Beneath the number was another carved message. Papa read out loud, “RUE JACQUES.”

They were sixty feet below the Rue Jacques. It had been Rue Saint-Jacques before. The revolutionaries had come so far, all this way, to eradicate the Saint from the Jacques, though no one walked these underground tracks but the Inspectorate of Mines and smugglers of taxable goods. And La Flèche, leading sparrows out of Paris.

Papa read each plaque aloud as they passed, being a man given to stating the obvious, when he was not saying mad things. “45 G 1777.”

Poulet glanced at the carved plaque, then upward to the stone that arched overhead. There were symbols there in chalk. Greek letters and an arrow. Nothing obvious. He said, “It’s only pockets of mining this far north. They haven’t dug everywhere. If they didn’t quarry under the Rue Tessier, there’s nothing we can do. You know that.”

“Yes.”

They were close. Rue Saint-Jacques was close. There had been mining here, everywhere. As she passed arch-ways, she could feel deep caverns beyond that swallowed the edges of her father’s voice. The scrape of grit under their boots shushed away and died in there.

They stopped at 37 Rue Jacques. Papa held the compass in one hand and the map in the other and shuffled in an odd dance, fitting compass to map, the direction of a vibrating needle to reality. These were his own maps of Paris, hand-drawn. They were extraordinarily accurate maps, but they only showed the tallest 156 buildings in Paris.

Adrian and Jean-Paul, who hauled the heavy loads, stood with their packs pressed against the wall, resting. Picks and shovels clicked against the rock. Papa tapped the compass and frowned at a solid wall.

Do not let that be the direction of the convent. Not there. Not into solid rock. Please. There are so many excavations. Let there be one under Rue Tessier.

“We must go around.” With a spurt of decision, Papa led the way back as they had come, speaking all the while of magnetism. It came in lines, apparently. They were hot upon the trail of one.

It does not matter that he is mad. It does not matter whether I have been logical, or wise, or if I have made a reasonable decision. Guillaume’s life rests only on whether I have been lucky.

Poulet reached up to run his fingers along the roof of the passage as they walked. “You know we can’t dig through this. It’d take months to chisel upward, and they’d catch us at it. It’s not a path into the prisons. If we can’t find the well . . .”

“I am hoping rather desperately that we do find the well.”

Papa stopped. He closed the compass and put it away.

There was a great finality in the click of closing that brass case that held the compass.

“Here?” she asked.

“It cannot be known. It is a mistake to think everything can be known. Heraclitus wrote upon this. The fluxes of the lines of force within the earth—”

“Papa, is it here? This place?”

“I am telling you—one cannot know.”

Nothing could be more certain than the pointing of a compass. Long after she was dead and gone, a compass would point to the north. “If one cannot know, can one guess?”

“If it is a guess you want . . .” He shrugged. “Go fifty paces. That way.” He pointed. “The front gate of the convent is within a hundred yards of whatever rock you stand upon, fifty paces down that line.” He pursed his lips. “Probably.”

She carried her candle into the darkness, counting. I must believe this.

Jean-Paul followed. The circle of his candle overlapped her own. Where she stopped, he set down his pack and concerned himself with the practicalities of taking out candles and lighting them. They had brought a huge supply. One cannot bring too many candles into the quarries, just as one cannot carry too much water into a desert.

The convent was above them. Guillaume was sixty feet away, in the sunlight.

“We are beneath the Convent of Saint-Barthélémy.” She didn’t have to raise her voice to be heard. They came close to her. Small flames showed their faces, their hands, their chests. “There is a well in the convent. I watched them draw water only a few hours ago. It is a well from centuries ago. The well shaft reaches through this quarry into the water that lies below. It is not far from where we stand.” If I say this strongly enough, I will make it true. “All this digging,” she waved the hand that did not hold her candle, “came later. Long after the well.”

So much silence. It is a small world that contains only six people and an immense darkness and the horrible finality of rock. One could not imagine how much darkness spread beyond them in every direction. Oceans of dark.

“This is the story of this place,” she said. “When quarry workmen find wells, they back away. They leave the stone untouched all around the well. They make it one of these pillars. Or they build around the well shaft with cut stone and mortar. Our well, the well of the convent, lies within one of these thick walls or these columns of stone.”

No one spoke. There was nothing to say. She finished, most simply, “We will find it.”

Adrian dropped his pack at her feet. Like Jean-Paul, like Justine and Poulet, he began to light candles and secure them to the floor with drippings of their own wax. Five candles. A dozen. Two dozen. A circle of light grew around their supplies, small and stubborn as stars in the sky. They invaded the darkness, and made camp, and these were their sentinels.

Adrian came to her when he was done. “So I’m looking for a patched-up hole in one of these big pillars, or a bit of wall that doesn’t make sense. Right?”

“Just so.” They might spend a week looking. Guillaume had one day. Perhaps two. Did everyone here know how small the chances were?

“What kind of idiots build a city on eggshells? Somebody sneezes and the whole place is going to fall in.” Adrian went off, shaking his head. “Paris.”

Poulet drank wine from his flask, corked it, and stowed it in the leather pack he carried. He raised his voice. “Don’t go where you can’t see somebody’s light. If you get lost, sit down and wait. I might even come looking for you. Bon courage.”

The first hour was spent searching every pillar and wall of that gallery, minutely, for any sign. They moved beyond, then, and lit their way into the next gallery and searched that.

In the fifth hour, they stopped to eat in a domed niche cut within the rocks. They ate on the circles of steps that led down to where water lived within the rocks. Eight feet below them lay a round pool, the drinking water, and perhaps the footbath, of the old quarrymen. It was water of such complete clarity it almost did not exist, except that it reflected back the flame of their candles. They ate the excellent tarts and cheeses served in the whorehouse and drank wine and spoke very little to one another.

Papa was tiring. She had made him bring a warm coat, but he was chilled. It would be late afternoon in the outside world.

Their tenth hour under the earth, six o’clock in the evening, they had traced and retraced and circled the center of their search and were in a new gallery. Bats spiraled upward and escaped through some vent in the arched ceiling. A weak shaft of light infiltrated from far above and struck all the way down to the cavern floor, fresh and beautiful as a spring in the desert.

It was a ventilation shaft, drilled in the rock. She went to it as if pulled by strings and stood in the light and looked up. She had been in darkness for a century.

“I’ll track this, up top, and find it,” Poulet said. “It’ll show exactly where we are. But that’s going to take a day or two. It probably comes up in somebody’s garden.”

They stood, all of them, looking up.

“It’ll be big enough for a man to go through, lowered by a rope. Always good to have one more entrance,” Poulet said.