“The great artist Doré,” the man announced. “His spectacularly grim interpretation of Dante Alighieri’s vision of hell. I hope it looks comfortable to you … because that’s where we’re headed.” He paused, drifting slowly toward her. “And let me tell you why.”

He kept moving toward her, seeming to grow taller with every step. “If I were to take this piece of paper and tear it in two …” He paused at a table, picked up a sheet of paper, and ripped it loudly in half. “And then if I were to place the two halves on top of each other …” He stacked the two halves. “And then if I were to repeat the process …” He again tore the papers, stacking them. “I produce a stack of paper that is now four times the thickness of the original, correct?” His eyes seemed to smolder in the darkness of the room.

Elizabeth did not appreciate his condescending tone and aggressive posture. She said nothing.

“Hypothetically speaking,” he continued, moving closer still, “if the original sheet of paper is a mere one-tenth of a millimeter thick, and I were to repeat this process … say, fifty times … do you know how tall this stack would be?”

Elizabeth bristled. “I do,” she replied with more hostility than she intended. “It would be one-tenth of a millimeter times two to the fiftieth power. It’s called geometric progression. Might I ask what I’m doing here?”

The man smirked and gave an impressed nod. “Yes, and can you guess what that actual value might look like? One-tenth of a millimeter times two to the fiftieth power? Do you know how tall our stack of paper has become?” He paused only an instant. “Our stack of paper, after only fifty doublings, now reaches almost all the way … to the sun.”

Elizabeth was not surprised. The staggering power of geometric growth was something she dealt with all the time in her work. Circles of contamination … replication of infected cells … death-toll estimates. “I apologize if I seem naive,” she said, making no effort to hide her annoyance. “But I’m missing your point.”

“My point?” He chuckled quietly. “My point is that the history of our human population growth is even more dramatic. The earth’s population, like our stack of paper, had very meager beginnings … but alarming potential.”

He was pacing again. “Consider this. It took the earth’s population thousands of years—from the early dawn of man all the way to the early 1800s—to reach one billion people. Then, astoundingly, it took only about a hundred years to double the population to two billion in the 1920s. After that, it took a mere fifty years for the population to double again to four billion in the 1970s. As you can imagine, we’re well on track to reach eight billion very soon. Just today, the human race added another quarter-million people to planet Earth. A quarter million. And this happens every day—rain or shine. Currently, every year, we’re adding the equivalent of the entire country of Germany.”

The tall man stopped short, hovering over Elizabeth. “How old are you?”

Another offensive question, although as the head of the WHO, she was accustomed to handling antagonism with diplomacy. “Sixty-one.”

“Did you know that if you live another nineteen years, until the age of eighty, you will witness the population triple in your lifetime. One lifetime—a tripling. Think of the implications. As you know, your World Health Organization has again increased its forecasts, predicting there will be some nine billion people on earth before the midpoint of this century. Animal species are going extinct at a precipitously accelerated rate. The demand for dwindling natural resources is skyrocketing. Clean water is harder and harder to come by. By any biological gauge, our species has exceeded our sustainable numbers. And in the face of this disaster, the World Health Organization—the gatekeeper of the planet’s health—is investing in things like curing diabetes, filling blood banks, battling cancer.” He paused, staring directly at her. “And so I brought you here to ask you directly why the hell the World Health Organization does not have the guts to deal with this issue head-on?”

Elizabeth was seething now. “Whoever you are, you know damned well the WHO takes overpopulation very seriously. Recently we spent millions of dollars sending doctors into Africa to deliver free condoms and educate people about birth control.”

“Ah, yes!” the lanky man derided. “And an even bigger army of Catholic missionaries marched in on your heels and told the Africans that if they used the condoms, they’d all go to hell. Africa has a new environmental issue now—landfills overflowing with unused condoms.”

Elizabeth strained to hold her tongue. He was correct on this point, and yet modern Catholics were starting to fight back against the Vatican’s meddling in reproductive issues. Most notably, Melinda Gates, a devout Catholic herself, had bravely risked the wrath of her own church by pledging $560 million to help improve access to birth control around the world. Elizabeth Sinskey had gone on record many times saying that Bill and Melinda Gates deserved to be canonized for all they’d done through their foundation to improve world health. Sadly, the only institution capable of conferring sainthood somehow failed to see the Christian nature of their efforts.

“Dr. Sinskey,” the shadow continued. “What the World Health Organization fails to recognize is that there is only one global health issue.” He pointed again to the grim image on the screen—a sea of tangled, cloying humanity. “And this is it.” He paused. “I realize you are a scientist, and therefore perhaps not a student of the classics or the fine arts, so let me offer another image that may speak to you in a language you can better understand.”

The room went dark for an instant, and the screen refreshed.

The new image was one Elizabeth had seen many times … and it always brought an eerie sense of inevitability.

A heavy silence settled in the room.

“Yes,” the lanky man finally said. “Silent terror is an apt response to this graph. Seeing it is a bit like staring into the headlight of an oncoming locomotive.” Slowly, the man turned to Elizabeth and gave her a tight, condescending smile. “Any questions, Dr. Sinskey?”

“Just one,” she fired back. “Did you bring me here to lecture me or insult me?”

“Neither.” His voice turned eerily cajoling. “I brought you here to work with you. I have no doubt you understand that overpopulation is a health issue. But what I fear you don’t understand is that it will affect the very soul of man. Under the stress of overpopulation, those who have never considered stealing will become thieves to feed their families. Those who have never considered killing will kill to provide for their young. All of Dante’s deadly sins—greed, gluttony, treachery, murder, and the rest—will begin percolating … rising up to the surface of humanity, amplified by our evaporating comforts. We are facing a battle for the very soul of man.”

“I’m a biologist. I save lives … not souls.”

“Well, I can assure you that saving lives will become increasingly difficult in the coming years. Overpopulation breeds far more than spiritual discontent. There is a passage in Machiavelli—”

“Yes,” she interrupted, reciting her recollection of the famous quote. “ ‘When every province of the world so teems with inhabitants that they can neither subsist where they are nor remove themselves elsewhere … the world will purge itself.’ ” She stared up at him. “All of us at the WHO are familiar with that quotation.”

“Good, then you know that Machiavelli went on to talk about plagues as the world’s natural way of self-purging.”

“Yes, and as I mentioned in my talk, we are well aware of the direct correlation between population density and the likelihood of wide-scale epidemics, but we are constantly devising new detection and treatment methods. The WHO remains confident that we can prevent future pandemics.”

“That’s a pity.”

Elizabeth stared in disbelief. “I beg your pardon?!”

“Dr. Sinskey,” the man said with a strange laugh, “you talk about controlling epidemics as if it’s a good thing.”

She gaped up at the man in mute disbelief.

“There you have it,” the lanky man declared, sounding like an attorney resting his case. “Here I stand with the head of the World Health Organization—the best the WHO has to offer. A terrifying thought if you consider it. I have shown you this image of impending misery.” He refreshed the screen, again displaying the image of the bodies. “I have reminded you of the awesome power of unchecked population growth.” He pointed to his small stack of paper. “I have enlightened you about the fact that we are on the brink of a spiritual collapse.” He paused and turned directly toward her. “And your response? Free condoms in Africa.” The man gave a derisive sneer. “This is like swinging a flyswatter at an incoming asteroid. The time bomb is no longer ticking. It has already gone off, and without drastic measures, exponential mathematics will become your new God … and ‘He’ is a vengeful God. He will bring to you Dante’s vision of hell right outside on Park Avenue … huddled masses wallowing in their own excrement. A global culling orchestrated by Nature herself.”

“Is that so?” Elizabeth snapped. “So tell me, in your vision of a sustainable future, what is the ideal population of earth? What is the magic number at which humankind can hope to sustain itself indefinitely … and in relative comfort?”

The tall man smiled, clearly appreciating the question. “Any environmental biologist or statistician will tell you that humankind’s best chance of long-term survival occurs with a global population of around four billion.”

“Four billion?” Elizabeth fired back. “We’re at seven billion now, so it’s a little late for that.”

The tall man’s green eyes flashed fire. “Is it?”

CHAPTER 23

Robert Langdon landed hard on the spongy earth just inside the retaining wall of the Boboli Gardens’ heavily wooded southern edge. Sienna landed beside him and stood up, brushing herself off and taking in their surroundings.

They were standing in a glade of moss and ferns on the edge of a small forest. From here, the Palazzo Pitti was entirely obscured from view, and Langdon sensed they were about as far from the palace as one could get in the gardens. At least there were no workers or tourists out this far at this early hour.

Langdon gazed at a peastone pathway that wound gracefully downhill into the forest before them. At the point where the path disappeared into the trees, a marble statue had been perfectly situated to receive the eye. Langdon was not surprised. The Boboli Gardens had enjoyed the exceptional design talents of Niccolò Tribolo, Giorgio Vasari, and Bernardo Buontalenti—a brain trust of aesthetic talent that had created on this 111-acre canvas a walkable masterpiece.

“If we head northeast, we’ll reach the palace,” Langdon said, pointing down the path. “We can mix there with the tourists and exit unseen. I’m guessing it opens at nine.”

Langdon glanced down to check the time but saw only his bare wrist where his Mickey Mouse watch had once been strapped. He wondered absently if it was still at the hospital with the rest of his clothing and if he’d ever be able to retrieve it.

Sienna planted her feet defiantly. “Robert, before we take another step, I want to know where we’re going. What did you figure out back there? The Malebolge? You said it was out of sequence?”

Langdon motioned toward a wooded area just ahead. “Let’s get out of sight first.” He led her down a pathway that curled into an enclosed hollow—a “room,” in the parlance of landscape architecture—where there were some faux-bois benches and a small fountain. The air beneath the trees was decidedly colder.

Langdon took the projector from his pocket and began shaking it. “Sienna, whoever created this digital image not only added letters to the sinners in the Malebolge, but he also changed the order of the sins.” He hopped up on the bench, towering over Sienna, and aimed the projector down at his feet. Botticelli’s Mappa dell’Inferno materialized faintly on the flat bench top beside Sienna.

Langdon motioned to the tiered area at the bottom of the funnel. “See the letters in the ten ditches of the Malebolge?”

Sienna found them on the projection and read from top to bottom. “Catrovacer.”

“Right. Meaningless.”

“But then you realized the ten ditches had been shuffled around?”

“Easier than that, actually. If these levels were a deck of ten cards, the deck was not so much shuffled as simply cut once. After the cut, the cards remain in the correct order, but they start with the wrong card.” Langdon pointed down at the ten ditches of the Malebolge. “According to Dante’s text, our top level should be the seducers whipped by demons. And yet, in this version, the seducers appear … way down in the seventh ditch.”

Sienna studied the now-fading image beside her and nodded. “Okay, I see that. The first ditch is now the seventh.”

Langdon pocketed the projector and jumped back down onto the pathway. He grabbed a small stick and began scratching letters on a patch of dirt just off the path. “Here are the letters as they appear in our modified version of hell.”

“Catrovacer,” Sienna read.

“Yes. And here is where the ‘deck’ was cut.” Langdon now drew a line beneath the seventh letter and waited while Sienna studied his handiwork.

“Okay,” she said quickly. “Catrova. Cer.”

“Yes, and to put the cards back in order, we simply uncut the deck and place the bottom on top. The two halves swap places.”