The WHO director had just finished coordinating an array of emergency meetings to be held in Geneva in several hours. Specialists from various agencies were already en route, and Sinskey herself planned to fly there shortly to brief them. Mercifully, someone on the night staff had delivered a piping-hot mug of authentic Turkish coffee, which Sinskey had quickly drained.

A young man on the consulate staff peered in her open door. “Ma’am? Robert Langdon is here to see you.”

“Thank you,” she replied. “You can send him in.”

Twenty minutes earlier, Langdon had contacted Sinskey by phone and explained that Sienna Brooks had eluded him, having stolen a boat and fled out to sea. Sinskey had already heard this news from the authorities, who were still searching the area, but so far had come up empty-handed.

Now, as Langdon’s tall frame materialized in the doorway, she barely recognized him. His suit was dirty, his dark hair tousled, and his eyes looked weary and sunken.

“Professor, are you okay?” Sinskey stood up.

Langdon gave her a tired smile. “I’ve had easier nights.”

“Please,” she said, motioning to a chair. “Have a seat.”

“Zobrist’s contagion,” Langdon began without preamble as he sat down. “I think it may have been released a week ago.”

Sinskey gave a patient nod. “Yes, we’ve come to the same conclusion. No symptoms have been reported yet, but we’ve isolated samples and are already gearing up for intensive testing. Unfortunately, it could take days or weeks to get a real grip on what this virus is … and what it might do.”

“It’s a vector virus,” Langdon said.

Sinskey cocked her head in surprise, startled to hear that he even knew the term. “I beg your pardon?”

“Zobrist created an airborne vector virus capable of modifying human DNA.”

Sinskey rose abruptly, knocking her chair over in the process. That’s not even possible! “What would ever make you claim such a thing?”

“Sienna,” Langdon replied quietly. “She told me. Half an hour ago.”

Sinskey leaned her hands on her desk and stared across at Langdon with sudden distrust. “She didn’t escape?”

“She certainly did,” he replied. “She was free, in a boat speeding out to sea, and she easily could have disappeared forever. But she thought better of it. She came back of her own volition. Sienna wants to help with this crisis.”

A harsh laugh escaped Sinskey’s lips. “Forgive me if I’m not inclined to trust Ms. Brooks, especially when she’s making such a far-fetched claim.”

“I believe her,” Langdon said, his tone unwavering. “And if she claims that this is a vector virus, I think you’d better take her seriously.”

Sinskey felt suddenly exhausted, her mind struggling to analyze Langdon’s words. She moved to the window and stared out. A DNA-altering viral vector? As improbable and horrifying as the prospect sounded, she had to admit there was an eerie logic to it. After all, Zobrist was a genetic engineer and knew firsthand that the smallest mutation in a single gene could have catastrophic effects on the body — cancers, organ failure, and blood disorders. Even a disease as abhorrent as cystic fibrosis — which drowns its victim in mucus — was caused by nothing more than a minuscule hiccup in a regulator gene on chromosome seven.

Specialists had now started treating these genetic conditions with rudimentary vector viruses that were injected directly into the patient. These noncontagious viruses were programmed to travel through the patient’s body and install replacement DNA that fixed the damaged sections. This new science, however, like all sciences, had a dark side. The effects of a vector virus could be either favorable or destructive … depending on the engineer’s intentions. If a virus were maliciously programmed to insert damaged DNA into healthy cells, the results would be devastating. Moreover, if that destructive virus were somehow engineered to be highly contagious and airborne …

The prospect made Sinskey shudder. What genetic horror has Zobrist dreamed up? How does he plan to thin the human herd?

Sinskey knew that finding the answer could take weeks. The human genetic code contained a seemingly infinite labyrinth of chemical permutations. The prospect of searching its entirety in hopes of finding Zobrist’s one specific alteration would be like looking for a needle in a haystack … without even knowing on what planet that particular haystack was located.

“Elizabeth?” Langdon’s deep voice pulled her back.

Sinskey turned from the window and looked at him.

“Did you hear me?” he asked, still seated calmly. “Sienna wanted to destroy this virus as much as you did.”

“I sincerely doubt that.”

Langdon exhaled, standing now. “I think you should listen to me. Shortly before his death, Zobrist wrote a letter to Sienna, telling her what he had done. He outlined exactly what this virus would do … how it would attack us … how it would achieve his goals.”

Sinskey froze. There’s a letter?!

“When Sienna read Zobrist’s description of what he had created, she was horrified. She wanted to stop him. She considered his virus so dangerous that she didn’t want anybody to gain access to it, including the World Health Organization. Don’t you see? Sienna has been trying to destroy the virus … not release it.”

“There’s a letter?” Sinskey demanded, her focus now singular. “With specifics?”

“That’s what Sienna told me, yes.”

“We need that letter! Having specifics could save us months in understanding what this thing is and knowing how to handle it.”

Langdon shook his head. “You don’t understand. When Sienna read Zobrist’s letter, she was terrified. She burned it immediately. She wanted to be sure nobody—”

Sinskey smacked her hand down on the desk. “She destroyed the one thing that could help us prepare for this crisis? And you want me to trust her?”

“I know it’s asking a lot, in light of her actions, but rather than castigating her, it might be helpful to remember that Sienna has a unique intellect, including a rather startling capacity for recall.” Langdon paused. “What if she can re-create enough of Zobrist’s letter to be helpful to you?”

Sinskey narrowed her gaze, nodding slightly. “Well, Professor, in that case, what do you suggest I do?”

Langdon motioned to her empty coffee cup. “I suggest you order more coffee … and listen to the one condition that Sienna has requested.”

Sinskey’s pulse quickened, and she glanced at the phone. “You know how to reach her?”

“I do.”

“Tell me what she requested.”

Langdon told her, and Sinskey fell silent, considering the proposal.

“I think it’s the right thing to do,” Langdon added. “And what do you have to lose?”

“If everything you’re saying is true, then you have my word.” Sinskey pushed the phone toward him. “Please make the call.”

To Sinskey’s surprise, Langdon ignored the phone. Instead, he stood up and headed out the door, stating that he would be back in a minute. Puzzled, Sinskey walked into the hall and observed him striding through the consulate’s waiting area, pushing open the glass doors, and exiting into the elevator foyer beyond. For a moment, she thought he was leaving, but then, rather than summoning the elevator, he slipped quietly into the women’s restroom.

A few moments later, he emerged with a woman who looked to be in her early thirties. Sinskey needed a long moment to accept the fact that this was truly Sienna Brooks. The pretty ponytailed woman she had seen earlier in the day had been utterly transformed. She was totally bald, as if her scalp had been shaved clean.

When the two entered her office, they silently took seats facing the desk.

“Forgive me,” Sienna said quickly. “I know we have a lot to discuss, but first, I was hoping you would permit me to say something that I really need to say.”