He waited a moment as the tracker was activated. When the blinking dot appeared on the map of Prague, Kerble stared in confusion. The vehicle was most definitely not parked nearby, as expected. Instead, it was parked three miles away…on the ridgeline above Folimanka Park.

  Several stories underground, The Golěm strode across the SMES vault toward the twelve Cryofab tanks of liquid helium. The top of each massive flask terminated in a reinforced electronic bayonet and valve connected to an insulated pipe that fed the SMES. On the wall near the tanks glowed a control panel bearing a diagram of all twelve canisters and their various statuses.

  By all appearances, the screen regulated the flow of helium to each canister. The Golěm had no idea how to use this panel, nor did he have any intention of trying. What he was planning required no subtlety. There was a very simple way to halt the flow of the supercooled liquid into the SMES.

  He approached the first canister, a bulbous stainless-steel flask taller than he was. His clay-caked face reflected back at him. I am not a monster, he reminded himself, knowing his outer shell, like everyone’s, was a mirage that shrouded the truth within. I am her protector.

  As expected, at the top of each tank beside the clutter of electronic connectors and valves, there was a manual cutoff—a handwheel valve that one could turn in emergencies to stop the flow of helium.

  As simple as turning off a garden hose.

  According to everything he had read, the slow chain reaction would begin as soon as the flow of helium was halted, causing the superconducting coils to begin to heat up, losing some of their conductivity, resisting the current…and commencing a deadly feedback loop.

  Heat Resistance Heat Resistance Heat…

  Once I close the valves, he estimated, I’ll have about twenty minutes.

  After that time, the coils would heat up and reach critical temperature—the “quench limit” when all the liquid helium in the system would begin to boil…converting to gas. The Golěm pictured the quench vent above him, which was now sealed shut, and he imagined the rapidly expanding cloud of helium gas trying to escape safely in a geyser of icy helium vapor.

  No longer possible, he thought. Today will be a different scenario.

  The rapidly expanding gas cloud would find no escape and would begin applying enormous pressure to every square inch of this airtight chamber.

  Including on the rupture disks.

  The Golěm took a deep breath and surveyed the line of canisters. He could already imagine the pressure in the vault climbing…pressing out against the thick concrete walls…causing the rupture disks in each tank to fail. Very suddenly, there would be some twenty thousand liters of liquid helium exposed to open air.

  The chain reaction would be instantaneous and unstoppable—a catastrophic expansion event—as violent and destructive as igniting a powerful warhead in this small space.

  CHAPTER 108

  As he descended, Langdon found himself wishing their escape through the retracting wall had led to daylight, rather than to a ramp that spiraled deeper into the earth. While it was logical that a bomb shelter would have a lower level—after all, the nuclear command centers at Cheyenne Mountain and Yamantau Mountain were both built under more than a thousand feet of solid granite—Langdon had hoped to be carrying the evidence they had gathered up and out of Threshold…not farther into it.

  With luck, whoever had entered Threshold behind them was not a threat, but still Langdon and Katherine had wasted no time beginning their descent and putting distance between themselves and whoever was entering behind them. Having finally obtained the proof they needed, they now had to find their way out.

  Spiraling deeper, they reached the bottom of the ramp just as a frightening sound materialized above them—the rapid staccato of hard-soled shoes on concrete, moving at an accelerated pace. This was no janitor.

  “We need to go!” Langdon whispered.

  At the base of the ramp, there was another retractable wall, identical to the one above. They hurried through it and found themselves in an eerie corridor that was approximately thirty feet long. In the dim light, the matte-black walls, ceilings, and floors gave off the aura more of a mausoleum than a tech facility.

  “It’s a different world down here…” Katherine whispered.

  Wherever they now were, Langdon estimated they had less than twenty seconds to find a place to hide. The spiral ramp had left him increasingly disoriented, and the exit at Crucifix Bastion felt farther away with every step. Being spotted way down here, Langdon now feared, would result in an alarm being sounded, making escape nearly impossible.

  They jogged down the sepulchral hallway, passing a long window on their right, beyond which a sea of green and red pinpoint lights pulsed in the darkness. Langdon could just make out the silhouettes of dozens of massive computer racks housed inside a meshed cage.

  “Faraday shielding…” Katherine whispered. “Those computers must be quantum.”

  Langdon knew very little about quantum computers except that they required shielding from cosmic rays and other forms of radiation. Another reason why Threshold is underground?

  As they passed the computer room entrance, Katherine never slowed, apparently sharing Langdon’s instinct not to trap themselves inside a literal metal cage.

  The hallway took a sharp left, and as they rounded the corner, more soft lighting came on, illuminating a much longer section of similar black corridor.

  “There!” Katherine whispered, pointing to the far end of the hall.

  What lay ahead did indeed offer a ray of hope, but Langdon now heard the unmistakable sound of footsteps echoing behind them again.

  We’ll never make it in time.

  In the distance, the hallway terminated at a metal door, above which a message was emblazoned in the most efficient and universal language on earth—a symbol whose entire meaning was instantaneously conveyed.

  The symbol of the ascending staircase was a welcome sight, and Langdon felt confident that if they could climb back to the upper floor, they could find their way to the bastion exit the way they had come.

  But we can’t reach the stairs unseen, he thought, hearing the footsteps getting closer.

  The hallway ahead offered two other doorways, both on the right. Regrettably, Langdon could already see that neither would be of any help.

  The first door, just ahead, was marked SUPPLY ROOM. If it was anything like the medical supply room upstairs, the space was a long warren of shelving with automatic lights and no exit. A death trap.

  The second doorway, just beyond it, was much larger and set back several feet in a recessed alcove. Whatever lay beyond the door was apparently important, because Langdon could see from here that it was equipped with a familiar security device—a circular pad of black glass.

  An RFID scanner…for which we no longer have authorization.

  The footsteps behind them were getting loud.

  As they approached the supply room door, Langdon slowed to a stop as a thought materialized. One of the great mysteries of consciousness was where ideas came from. Katherine claimed the mind was a receiver that tuned into a greater field of consciousness. Gessner claimed the brain was a computer whose trillions of neural switches simply solved the problem.

  At the moment, Langdon didn’t care who was right. The source of his idea was irrelevant. All that mattered was that he suddenly knew exactly what to do.

  Why did he stop?!

  Katherine turned back to Langdon, who was opening the supply room door. It was obvious they could not reach the stairway at the end of the hall without being seen, but hiding in the supply room seemed like suicide.

  She hurried back to stop him, but Langdon had already stepped inside. The fluorescent lights directly above flickered on to illuminate the entrance to the narrow warren of shelves that extended away from them into darkness. Without hesitation, Langdon grabbed a bottle of liquid cleaner off the shelf and, like a bowler, slung the bottle down the aisle between the shelves. It skittered along the floor and slid all the way to the end without touching either side, triggering a series of motion lights into the deepest recesses of the supply room. Even before the bottle had hit the far wall, Langdon stepped back into the hall. He closed the door but left it open a crack, allowing a sliver of fluorescent light to spill into the dimly lit corridor. Then he grabbed Katherine’s hand and pulled her as quickly as possible in the direction they had been going, toward the stairwell door that was still at least forty yards away.

  As they ran, she felt buoyed by a sudden optimism, having just realized Langdon’s clever thinking. We don’t need to reach the end of the hall yet…

  As she anticipated, when they neared the recessed alcove with the RFID scanner, Langdon cut hard right, pulling Katherine with him into the alcove. The recess was shallow—less than three feet deep—and they spun around and stood with their backs against the cold metal of the heavy door, making themselves as tall and slender as possible, hoping the alcove was deep enough to conceal them from view.

  A moment later, the sound of footsteps entered the hall and stopped.

  There was a long silence.

  Then Katherine heard the unmistakable sound of a gun being cocked.

  Jonas Faukman’s eyes opened abruptly, and he realized he had drifted off at his desk. He was uncertain why he had awoken so suddenly—perhaps the sound of rain that was now pelting his window—but as he stood to stretch, he was surprised to feel the cool creep of returning dread.

  Everything is fine, he assured himself. RL&KSRGUD.

  CHAPTER 109

  Langdon and Katherine stood rigid, side by side and barely breathing. Their backs were quite literally against the wall, or more accurately, against an exceptionally wide steel door. Even though they had slipped into this recess undetected, their arrival had been accompanied by the unwelcome sound of a gun being cocked.

  Langdon remained still, hoping the fluorescent lights blazing in the supply room would be suspicious enough to warrant a search.

  We just need a minute’s distraction.

  If not…they were trapped.

  The footsteps slowly began again, moving closer. After several tense seconds, Langdon saw a welcome sight—a faint splash of fluorescent light on the far wall. Whoever is there opened the supply room door!

  Suddenly, the fluorescent lights disappeared, and Langdon heard the supply room door click shut. Did he go inside?! Langdon strained to hear footsteps, but there was only silence. Katherine shifted beside him, and he felt her hand trying to find his at his side. For a moment, he thought she was looking for emotional support, but then he felt her press a small object into his palm. He glanced down and saw a compact mirror, which she had just pulled from her bag.

  Langdon flipped the mirror open with his thumb and carefully extended it just an inch past the edge of the recess. In the tiny reflection, he hoped to see an empty hallway. But instead, he saw the unmistakable shape of a figure approaching, inching stealthily toward them. The man was older, with silver hair, a dark suit, and glasses.

  Whoever the man was, he had not been fooled. His handgun was raised, pointing in their direction.

  Everett Finch peered over the barrel of the outstretched SIG Sauer pistol and surveyed the hallway ahead. The intruder was near. Whoever had penetrated the lower level of Threshold had not come to hide in a supply closet; they had come for something else.

  And if they’ve made it this far, they’re perilously close to uncovering Threshold’s most sensitive secret.

  As Finch advanced, he maintained focus on the hallway’s lone hiding place—the recessed doorway ahead on the right, which was just deep enough to conceal anyone who was standing flush with the heavy metal door.

  Hugging the left-hand side of the corridor, he moved with furtive steps, keeping his gun trained on the alcove. As his angle improved, his sight line began to reveal the interior of the alcove. When he finally glimpsed the leftmost edge of the metal door, Finch surged forward with two long strides and crouched down, swinging his arms around and taking dead aim.

  To his surprise, the alcove was empty.

  Langdon and Katherine stood face-to-face, hearts pounding.

  What just happened?!

  Seconds ago, with their backs against the wide steel door, Langdon had recoiled from the reflection of a man advancing on them with a pistol. As he pressed up hard against the door, he felt suddenly as if he was losing his balance—but then Katherine’s eyes went wide with disbelief, and it dawned on Langdon what had just happened.

  The heavy door behind them…had moved.

  Langdon leaned back hard again, joined by Katherine. The door was spring-loaded and stiff, but as they braced their feet and thrust themselves backward, it swung open. It made no sense considering the presence of an RFID scanner, but as he and Katherine slipped through, Langdon noticed the strike plate in the doorjamb was stuffed with some kind of green fabric, apparently to keep it from locking.

  Who propped this door open?!

  Fearing the gunman in the hall, Langdon instinctively pulled the green material out of the strike plate and quietly let the door close. The portal clicked and engaged. Locked. The material in his hand, he now realized, was not fabric at all, but rather vinyl or rubber—a cluster of artificial leaves that must have been yanked off the fake ficus tree just inside the door.

  “Incredible luck,” Langdon whispered in amazement.

  Katherine looked less relieved than he expected. “Unless someone wanted to be sure they could get out.”

  “What do you mean?”

  She pointed to a second RFID scanner on the wall beside the ficus tree. “You also need a card to exit, Robert. Someone was trying to prop this door open…but we’ve just locked ourselves in.”

  The Golěm gripped the turn wheel on the fourth canister of helium and twisted it to the right, just as he had done with the first three. The end is near. After several tight turns, the valve was fully closed, and the control panel beeped urgently. The icon for canister #4 turned red. OFF. Four indicators in a row now glowed red with warning, alongside eight that still were illuminated green.

  He began the process anew for canister #5, laboring slowly as the wheel turned. OFF.

  The Golěm made his way down the line, turning off each valve. Every time he shut down a canister, the controller pinged and made an adjustment, opening the helium flow to the next fresh backup canister.

  Despite his eagerness to finish the job, The Golěm moved slowly and maintained slow, deep breathing to help prevent another seizure. His objective was within sight now, and he forced himself to be cautious. As he closed each valve, he rehearsed in his mind the steps he would take to escape.

  Twenty minutes will be plenty of time…

  A loud buzzer sounded now, pulling The Golěm back from his thoughts. The control panel was flashing warnings and emitting increasingly urgent beeps. The display screen showed eleven canisters were off. Every canister except #12 was now manually disconnected from the SMES. More importantly, nine of those canisters were listed as 100 percent full.

  Thousands of kilos of liquid helium in this tiny space.

  The Golěm took a deep breath and reviewed his plan one last time, then placed his hand on the turn wheel of #12.

  I do this for you, Sasha, he thought as he began closing the valve.

  Threshold was built with your blood.

  Our blood.

  The valve came to a stop, fully closed.

  And now I have destroyed it.

  At CIA headquarters in Langley, Director Judd sat alone in his secure communications room. He was trying to formulate the proper response to the horrifying video he had just witnessed. A tech team had already purged the video from the Internet, but that offered little solace; whoever had interrogated Gessner could simply repost it at any time.

  If this video leaked, Judd had little doubt it would go viral almost immediately—across the globe. Not only did it feature the brutal torture of a prominent scientist, but the video contained a confession that revealed the existence of a highly secret U.S. intelligence project…including its location…technological breakthroughs…and use of nonvoluntary human subjects.

  The fallout would be like nothing the CIA had ever experienced.

  CHAPTER 110

  Langdon surveyed the small room into which he and Katherine had just escaped.

  Whatever this place is…I’ve just locked us in.

  The space felt decidedly softer than the sterile corridor outside; it had carpeting, a number of realistic artificial trees, and even a series of abstract paintings on the wall. There was an arched opening ahead of them, and he eyed it with trepidation. Beyond, a wide concrete tunnel curved to the left and out of sight. Three things about the passage felt instantly ominous to Langdon.

  First, the tunnel lights were already on—pale blue on the gray walls—suggesting that someone else might already be inside. Second, the floor of the tunnel was inclined downward, and Langdon hesitated to venture deeper into the earth. And finally, it seemed clear from the RFID cards required to enter and exit this area that the tunnel likely led to the most secure area of Threshold—rather than to an exit.

  For a fleeting moment, Langdon wondered if the safest move would be to surrender, but he had a growing suspicion that the older, well-dressed man pursuing them might actually be Mr. Finch himself—a man who, according to the ambassador, took no prisoners and would stop at nothing to protect Threshold.

  We need somewhere to hide…now.

  Langdon caught up with Katherine partway down the tunnel, which they followed to another arched portico. This entrance was framed in elegant black stone, with a wide swinging door of frosted glass. The translucent surface was etched with a familiar image: