“They won’t recognize us. They’ll be looking for a blond girl and a dark-haired man.”

Langdon eyed her strangely. “Which is precisely what we are …”

Sienna shook her head, a melancholy resolve crossing her face. “I didn’t want you to see me like this, Robert, but unfortunately it’s what I look like at the moment.” Abruptly, Sienna reached up and grabbed a handful of her blond hair. Then she yanked down, and all of her hair slid off in a single motion.

Langdon recoiled, startled both by the fact that Sienna wore a wig and by her altered appearance without it. Sienna Brooks was in fact totally bald, her bare scalp smooth and pale, like a cancer patient undergoing chemotherapy. On top of it all, she’s ill?

“I know,” she said. “Long story. Now bend down.” She held up the wig, clearly intending to put it on Langdon’s head.

Is she serious? Langdon halfheartedly bent over, and Sienna wedged the blond hair onto his head. The wig barely fit, but she arranged it as best as she could. Then she stepped back and assessed him. Not quite satisfied, she reached up, loosened his tie, and slipped the loop up onto his forehead, retightening it like a bandanna and securing the ill-fitting wig to his head.

Sienna now set to work on herself, rolling up her pant legs and pushing her socks down around her ankles. When she stood up, she had a sneer on her lips. The lovely Sienna Brooks was now a punk-rock skinhead. The former Shakespearean actress’s transformation was startling.

“Remember,” she said, “ninety percent of personal recognition is body language, so when you move, move like an aging rocker.”

Aging, I can do, Langdon thought. Rocker, I’m not so sure.

Before Langdon could argue the point, Sienna had unbolted the tiny door and swung it open. She ducked low and exited onto the crowded cobblestone street. Langdon followed, nearly on all fours as he emerged into the daylight.

Aside from a few startled glances at the mismatched couple emerging from the tiny door in the foundation of Palazzo Vecchio, nobody gave them a second look. Within seconds, Langdon and Sienna were moving east, swallowed up by the crowd.

The man in the Plume Paris eyeglasses picked at his bleeding skin as he snaked through the crowd, keeping a safe distance behind Robert Langdon and Sienna Brooks. Despite their clever disguises, he had spotted them emerging from the tiny door on the Via della Ninna and had immediately known who they were.

He had tailed them only a few blocks before he got winded, his chest aching acutely, forcing him to take shallow breaths. He felt like he’d been punched in the sternum.

Gritting his teeth against the pain, he forced his attention back to Langdon and Sienna as he continued to follow them through the streets of Florence.

CHAPTER 50

The morning sun had fully risen now, casting long shadows down the narrow canyons that snaked between the buildings of old Florence. Shopkeepers had begun throwing open the metal grates that protected their shops and bars, and the air was heavy with the aromas of morning espresso and freshly baked cornetti.

Despite a gnawing hunger, Langdon kept moving. I’ve got to find the mask … and see what’s hidden on the back.

As Langdon led Sienna northward along the slender Via dei Leoni, he was having a hard time getting used to the sight of her bald head. Her radically altered appearance reminded him that he barely knew her. They were moving in the direction of Piazza del Duomo—the square where Ignazio Busoni had been found dead after placing his final phone call.

Robert, Ignazio had managed to say, breathless. What you seek is safely hidden. The gates are open to you, but you must hurry. Paradise Twenty-five. Godspeed.

Paradise Twenty-five, Langdon repeated to himself, still puzzled that Ignazio Busoni had recalled Dante’s text well enough to reference a specific canto off the top of his head. Something about that canto was apparently memorable to Busoni. Whatever it was, Langdon knew he would find out soon enough, as soon as he laid his hands on a copy of the text, which he could easily do at any number of locations up ahead.

His shoulder-length wig was beginning to itch now, and though he felt somewhat ridiculous in his disguise, he had to admit that Sienna’s impromptu styling had been an effective ruse. Nobody had given them a second look, not even the police reinforcements who had just rushed past them en route to the Palazzo Vecchio.

Sienna had been walking in total silence beside him for several minutes, and Langdon glanced over to make sure she was okay. She seemed miles away, probably trying to accept the fact that she had just killed the woman who had been chasing them.

“Lira for your thoughts,” he ventured lightly, hoping to pull her mind from the image of the spike-haired woman lying dead on the palazzo floor.

Sienna emerged slowly from her contemplations. “I was thinking of Zobrist,” she said slowly. “Trying to recall anything else I might know about him.”

“And?”

She shrugged. “Most of what I know is from a controversial essay he wrote a few years ago. It really stayed with me. Among the medical community, it instantly went viral.” She winced. “Sorry, bad choice of words.”

Langdon gave a grim chuckle. “Go on.”

“His essay essentially declared that the human race was on the brink of extinction, and that unless we had a catastrophic event that precipitously decreased global population growth, our species would not survive another hundred years.”

Langdon turned and stared at her. “A single century?”

“It was a pretty stark thesis. The predicted time frame was substantially shorter than previous estimates, but it was supported by some very potent scientific data. He made a lot of enemies by declaring that all doctors should stop practicing medicine because extending the human life span was only exacerbating the population problem.”

Langdon now understood why the article spread wildly through the medical community.

“Not surprisingly,” Sienna continued, “Zobrist was immediately attacked from all sides—politicians, clergy, the World Health Organization—all of whom derided him as a doomsayer lunatic who was simply trying to cause panic. They took particular umbrage at his statement that today’s youth, if they chose to reproduce, would have offspring that literally would witness the end of the human race. Zobrist illustrated his point with a ‘Doomsday Clock,’ which showed that if the entire span of human life on earth were compressed into a single hour … we are now in its final seconds.”

“I’ve actually seen that clock online,” Langdon said.

“Yes, well, it’s his, and it caused quite an uproar. The biggest backlash against Zobrist, however, came when he declared that his advances in genetic engineering would be far more helpful to mankind if they were used not to cure disease, but rather to create it.”

“What?!”

“Yes, he argued that his technology should be used to limit population growth by creating hybrid strains of disease that our modern medicine would be unable to cure.”

Langdon felt a rising dread as his mind conjured images of strange, hybrid “designer viruses” that, once released, were totally unstoppable.

“Over a few short years,” Sienna said, “Zobrist went from being the toast of the medical world to being a total outcast. An anathema.” She paused, a look of compassion crossing her face. “It’s really no wonder he snapped and killed himself. Even sadder because his thesis is probably correct.”

Langdon almost fell over. “I’m sorry—you think he’s right?!”

Sienna gave him a solemn shrug. “Robert, speaking from a purely scientific standpoint—all logic, no heart—I can tell you without a doubt that without some kind of drastic change, the end of our species is coming. And it’s coming fast. It won’t be fire, brimstone, apocalypse, or nuclear war … it will be total collapse due to the number of people on the planet. The mathematics is indisputable.”

Langdon stiffened.

“I’ve studied a fair amount of biology,” she said, “and it’s quite normal for a species to go extinct simply as a result of overpopulating its environment. Picture a colony of surface algae living in a tiny pond in the forest, enjoying the pond’s perfect balance of nutrients. Unchecked, they reproduce so wildly that they quickly cover the pond’s entire surface, blotting out the sun and thereby preventing the growth of the nutrients in the pond. Having sapped everything possible from their environment, the algae quickly die and disappear without a trace.” She gave a heavy sigh. “A similar fate could easily await mankind. Far sooner and faster than any of us imagine.”

Langdon felt deeply unsettled. “But … that seems impossible.”

“Not impossible, Robert, just unthinkable. The human mind has a primitive ego defense mechanism that negates all realities that produce too much stress for the brain to handle. It’s called denial.”

“I’ve heard of denial,” Langdon quipped blithely, “but I don’t think it exists.”

Sienna rolled her eyes. “Cute, but believe me, it’s very real. Denial is a critical part of the human coping mechanism. Without it, we would all wake up terrified every morning about all the ways we could die. Instead, our minds block out our existential fears by focusing on stresses we can handle—like getting to work on time or paying our taxes. If we have wider, existential fears, we jettison them very quickly, refocusing on simple tasks and daily trivialities.”

Langdon recalled a recent Web-tracking study of students at some Ivy League universities which revealed that even highly intellectual users displayed an instinctual tendency toward denial. According to the study, the vast majority of university students, after clicking on a depressing news article about arctic ice melt or species extinction, would quickly exit that page in favor of something trivial that purged their minds of fear; favorite choices included sports highlights, funny cat videos, and celebrity gossip.

“In ancient mythology,” Langdon offered, “a hero in denial is the ultimate manifestation of hubris and pride. No man is more prideful than he who believes himself immune to the dangers of the world. Dante clearly agreed, denouncing pride as the worst of the seven deadly sins … and punished the prideful in the deepest ring of the inferno.”

Sienna reflected a moment and then continued. “Zobrist’s article accused many of the world’s leaders of being in extreme denial … putting their heads in the sand. He was particularly critical of the World Health Organization.”

“I bet that went over well.”

“They reacted by equating him with a religious zealot on a street corner holding a sign that says ‘The End Is Near.’ ”

“Harvard Square has a couple of those.”

“Yes, and we all ignore them because none of us can imagine it will happen. But believe me, just because the human mind can’t imagine something happening … doesn’t mean it won’t.”

“You almost sound like you’re a fan of Zobrist’s.”

“I’m a fan of the truth,” she replied forcefully, “even if it’s painfully hard to accept.”

Langdon fell silent, again feeling strangely isolated from Sienna at the moment, trying to understand her bizarre combination of passion and detachment.

Sienna glanced over at him, her face softening. “Robert, look, I’m not saying Zobrist is correct that a plague that kills half the world’s people is the answer to overpopulation. Nor am I saying we should stop curing the sick. What I am saying is that our current path is a pretty simple formula for destruction. Population growth is an exponential progression occurring within a system of finite space and limited resources. The end will arrive very abruptly. Our experience will not be that of slowly running out of gas … it will be more like driving off a cliff.”

Langdon exhaled, trying to process everything he had just heard.

“Speaking of which,” she added, somberly pointing up in the air to their right, “I’m pretty sure that’s where Zobrist jumped.”

Langdon glanced up and saw that they were just passing the austere stone facade of the Bargello Museum to their right. Behind it, the tapered spire of the Badia tower rose above the surrounding structures. He stared at the top of the tower, wondering why Zobrist had jumped and hoped to hell it wasn’t because the man had done something terrible and hadn’t wanted to face what was coming.

“Critics of Zobrist,” Sienna said, “like to point out how paradoxical it is that many of the genetic technologies he developed are now extending life expectancy dramatically.”

“Which only compounds the population problem.”

“Exactly. Zobrist once said publicly that he wished he could put the genie back in the bottle and erase some of his contributions to human longevity. I suppose that makes sense ideologically. The longer we live, the more our resources go to supporting the elderly and ailing.”

Langdon nodded. “I’ve read that in the U.S. some sixty percent of health care costs go to support patients during the last six months of their lives.”

“True, and while our brains say, ‘This is insane,’ our hearts say, ‘Keep Grandma alive as long as we can.’ ”

Langdon nodded. “It’s the conflict between Apollo and Dionysus—a famous dilemma in mythology. It’s the age-old battle between mind and heart, which seldom want the same thing.”

The mythological reference, Langdon had heard, was now being used in AA meetings to describe the alcoholic who stares at a glass of alcohol, his brain knowing it will harm him, but his heart craving the comfort it will provide. The message apparently was: Don’t feel alone—even the gods were conflicted.

“Who needs agathusia?” Sienna whispered suddenly.

“I’m sorry?”

Sienna glanced up. “I finally remembered the name of Zobrist’s essay. It was called: ‘Who Needs Agathusia?’ ”