athedral College is an elegant, castlelike edifice located adjacent to the National Cathedral. The College of Preachers, as it was originally envisioned by the first Episcopal bishop of Washington, was founded to provide ongoing education for clergy after their ordination. Today, the college offers a wide variety of programs on theology, global justice, healing, and spirituality.

Langdon and Katherine had made the dash across the lawn and used Galloway’s key to slip inside just as the helicopter rose back over the cathedral, its floodlights turning night back into day. Now, standing breathless inside the foyer, they surveyed their surroundings. The windows provided sufficient illumination, and Langdon saw no reason to turn the lights on and take a chance of broadcasting their whereabouts to the helicopter overhead. As they moved down the central hallway, they passed a series of conference halls, classrooms, and sitting areas. The interior reminded Langdon of the neo-Gothic buildings of Yale University—breathtaking on the outside, and yet surprisingly utilitarian on the inside, their period elegance having been retrofitted to endure heavy foot traffic.

“Down here,” Katherine said, motioning toward the far end of the hall.

Katherine had yet to share with Langdon her new revelation regarding the pyramid, but apparently the reference to Isaacus Neutonuus had sparked it. All she had said as they crossed the lawn was that the pyramid could be transformed using simple science. Everything she needed, she believed, could probably be found in this building. Langdon had no idea what she needed or how Katherine intended to transform a solid piece of granite or gold, but considering he had just witnessed a cube metamorphose into a Rosicrucian cross, he was willing to have faith.

They reached the end of the hall and Katherine frowned, apparently not seeing what she wanted. “You said this building has dormitory facilities?”

“Yes, for residential conferences.”

“So they must have a kitchen in here somewhere, right?”

“You’re hungry?”

She frowned back at him. “No, I need a lab.”

Of course you do. Langdon spotted a descending staircase that bore a promising symbol. America’s favorite pictogram.

The basement kitchen was industrial looking—lots of stainless steel and big bowls—clearly designed to cook for large groups. The kitchen had no windows. Katherine closed the door and flipped on the lights. The exhaust fans came on automatically.

She began rooting around in the cupboards for whatever it was she needed. “Robert,” she directed, “put the pyramid out on the island, if you would.”

Feeling like the novice sous chef taking orders from Daniel Boulud, Langdon did as he was told, removing the pyramid from his bag and placing the gold capstone on top of it. When he finished, Katherine was busy filling an enormous pot with hot tap water.

“Would you please lift this to the stove for me?”

Langdon heaved the sloshing pot onto the stove as Katherine turned on the gas burner and cranked up the flame.

“Are we doing lobsters?” he asked hopefully.

“Very funny. No, we’re doing alchemy. And for the record, this is a pasta pot, not a lobster pot.” She pointed to the perforated strainer insert that she had removed from the pot and placed on the island beside the pyramid.

Silly me. “And boiling pasta is going to help us decipher the pyramid?”

Katherine ignored the comment, her tone turning serious. “As I’m sure you know, there is a historical and symbolic reason the Masons chose thirty-three as their highest degree.”

“Of course,” Langdon said. In the days of Pythagoras, six centuries before Christ, the tradition of numerology hailed the number 33 as the highest of all the Master Numbers. It was the most sacred figure, symbolizing Divine Truth. The tradition lived on within the Masons . . . and elsewhere. It was no coincidence that Christians were taught that Jesus was crucified at age thirty-three, despite no real historical evidence to that effect. Nor was it coincidence that Joseph was said to have been thirty-three when he married the Virgin Mary, or that Jesus accomplished thirty-three miracles, or that God’s name was mentioned thirty-three times in Genesis, or that, in Islam, all the dwellers of heaven were permanently thirty-three years old.

“Thirty-three,” Katherine said, “is a sacred number in many mystical traditions.”

“Correct.” Langdon still had no idea what this had to do with a pasta pot.

“So it should come as no surprise to you that an early alchemist, Rosicrucian, and mystic like Isaac Newton also considered the number thirty-three special.”

“I’m sure he did,” Langdon replied. “Newton was deep into numerology, prophecy, and astrology, but what does—”

“All is revealed at the thirty-third degree.”

Langdon pulled Peter’s ring from his pocket and read the inscription. Then he glanced back at the pot of water. “Sorry, you lost me.”

“Robert, earlier tonight, we all assumed ‘thirty-third degree’ referred to the Masonic degree, and yet when we rotated that ring thirty-three degrees, the cube transformed and revealed a cross. At that moment, we realized the word degree was being used in another sense.”

“Yes. Degrees of arc.”

“Exactly. But degree has a third meaning as well.”

Langdon eyed the pot of water on the stove. “Temperature.”

“Exactly!” she said. “It was right in front of us all night. ‘All is revealed at the thirty-third degree.’ If we bring this pyramid’s temperature to thirty-three degrees . . . it may just reveal something.”

Langdon knew Katherine Solomon was exceptionally bright, and yet she seemed to be missing a rather obvious point. “If I’m not mistaken, thirty-three degrees is almost freezing. Shouldn’t we be putting the pyramid in the freezer?”

Katherine smiled. “Not if we want to follow the recipe written by the great alchemist and Rosicrucian mystic who signed his papers Jeova Sanctus Unus.”

Isaacus Neutonuus wrote recipes?

“Robert, temperature is the fundamental alchemical catalyst, and it was not always measured in Fahrenheit and Celsius. There are far older temperature scales, one of them invented by Isaac—”

“The Newton Scale!” Langdon said, realizing she was right.

“Yes! Isaac Newton invented an entire system of quantifying temperature based entirely on natural phenomena. The temperature of melting ice was Newton’s base point, and he called it ‘the zeroth degree.’ ” She paused. “I suppose you can guess what degree he assigned the temperature of boiling water—the king of all alchemical processes?”

“Thirty-three.”

“Yes, thirty-three! The thirty-third degree. On the Newton Scale, the temperature of boiling water is thirty-three degrees. I remember asking my brother once why Newton chose that number. I mean, it seemed so random. Boiling water is the most fundamental alchemical process, and he chose thirty-three? Why not a hundred? Why not something more elegant? Peter explained that, to a mystic like Isaac Newton, there was no number more elegant than thirty-three.”

All is revealed at the thirty-third degree. Langdon glanced at the pot of water and then over at the pyramid. “Katherine, the pyramid is made out of solid granite and solid gold. Do you really think boiling water is hot enough to transform it?”

The smile on her face told Langdon that Katherine knew something he did not know. Confidently, she walked over to the island, lifted the gold-capped, granite pyramid, and set it in the strainer. Then she carefully lowered it into the bubbling water. “Let’s find out, shall we?”

High above the National Cathedral, the CIA pilot locked the helicopter in auto-hover mode and surveyed the perimeter of the building and the grounds. No movement. His thermal imaging couldn’t penetrate the cathedral stone, and so he couldn’t tell what the team was doing inside, but if anyone tried to slip out, the thermal would pick it up.

It was sixty seconds later that a thermal sensor pinged. Working on the same principle as home-security systems, the detector had identified a strong temperature differential. Usually this meant a human form moving through a cool space, but what appeared on the monitor was more of a thermal cloud, a patch of hot air drifting across the lawn. The pilot found the source, an active vent on the side of Cathedral College.

Probably nothing, he thought. He saw these kinds of gradients all the time. Someone cooking or doing laundry. As he was about to turn away, though, he realized something odd. There were no cars in the parking lot and no lights on anywhere in the building.

He studied the UH-60’s imaging system for a long moment. Then he radioed down to his team leader. “Simkins, it’s probably nothing, but . . .”

“Incandescent temperature indicator!” Langdon had to admit, it was clever.

“It’s simple science,” Katherine said. “Different substances incandesce at different temperatures. We call them thermal markers. Science uses these markers all the time.”

Langdon gazed down at the submerged pyramid and capstone. Wisps of steam were beginning to curl over the bubbling water, although he was not feeling hopeful. He glanced at his watch, and his heart rate accelerated: 11:45 P.M. “You believe something here will luminesce as it heats up?”

“Not luminesce, Robert. Incandesce. There’s a big difference. Incandescence is caused by heat, and it occurs at a specific temperature. For example, when steel manufacturers temper beams, they spray a grid on them with a transparent coating that incandesces at a specific target temperature so they know when the beams are done. Think of a mood ring. Just put it on your finger, and it changes color from body heat.”

“Katherine, this pyramid was built in the 1800s! I can understand a craftsman making hidden release hinges in a stone box, but applying some kind of transparent thermal coating?”

“Perfectly feasible,” she said, glancing hopefully at the submerged pyramid. “The early alchemists used organic phosphors all the time as thermal markers. The Chinese made colored fireworks, and even the Egyptians—” Katherine stopped midsentence, staring intently into the roiling water.

“What?” Langdon followed her gaze into the turbulent water but saw nothing at all.

Katherine leaned in, staring more intently into the water. Suddenly she turned and ran across the kitchen toward the door.

“Where are you going?” Langdon shouted.

She slid to a stop at the kitchen light switch, flipped it off. The lights and exhaust fan went off, plunging the room into total darkness and silence. Langdon turned back to the pyramid and peered through the steam at the capstone beneath the water. By the time Katherine made it back to his side, his mouth had fallen open in disbelief.

Exactly as Katherine had predicted, a small section of the metal capstone was starting to glow beneath the water. Letters were starting to appear, and they were getting brighter as the water heated up.

“Text!” Katherine whispered.

Langdon nodded, dumbstruck. The glowing words were materializing just beneath the engraved inscription on the capstone. It looked like only three words, and although Langdon could not yet read what the words said, he wondered if they would unveil everything they had been looking for tonight. The pyramid is a real map, Galloway had told them, and it points to a real location.

As the letters shone brighter, Katherine turned off the gas, and the water slowly stopped churning. The capstone now came into focus beneath the water’s calm surface.

Three shining words were clearly legible.