In fact, she continues, the Mad Dog virus appears to have preceded the HK Lyssa virus. It is HK Lyssa's primitive ancestor. HK Lyssa is essentially a benign mutation of the Mad Dog virus that allowed it to survive by spreading more easily among humans.

"But in a few cases, HK Lyssa attacks the brain," she adds. "Once in the brain, the virus displays a remarkable trait: It reverts back to its primitive ancestor, the Mad Dog virus. HK Lyssa is therefore a-what is the term-Trojan Horse for Mad Dog. As you can see, we are wasting our time here trying to cure HK Lyssa."

"h.e.l.l, we've already isolated the b.a.s.t.a.r.d in vitro and we're working up a complete genetic characterization," says Hardy. "Don't be too hard on us. We have a ways to go, but we are getting close."

"What I am saying is we are trying to cure the wrong disease," she says.

"Bulls.h.i.+t," Hardy says flatly.

She stomps her right foot in frustration and says, "Oh!"

"What you're saying is fascinating, but academic. You said yourself that Mad Dog comes from Lyssa, so if we cure Lyssa, we cure Mad Dog."

"Doctor, listen to me carefully," Petrova tells him. "You know that Mad Dog and HK Lyssa come from the Lyssavirus family. Rabies is in that same family. While genetically very different, the symptoms are similar. The Mad Dog virus appears to be perfectly designed to transmit itself through bites and infected saliva. This is why the Mad Dog victim is so aggressive. He is compelled to seek out and infect others. This is an entirely new vector of disease transmission and, in my opinion, poses the greater threat."

Hardy grunts, interested now. "How does the virus operate?"

"When a Mad Dog bites an uninfected individual, the virus enters the body through the bite. It attacks the nerves and, undetected by the immune system, travels to the spinal cord. From there, it is mainlined to the brain. By the time the immune system detects the virus, it is too late. Very similar to rabies."

Hardy scratches his head in wonder. There were anecdotal reports of Mad Dogs transmitting illness through their saliva, but no real research in that area. The medical research community has been focused entirely on Hong Kong Lyssa as an airborne, flulike illness, and there were so few Mad Dogs. . . .

"What's the incubation period?" he asks her.

"It could be remarkably fast. My results suggest infection occurs within one hour and symptoms manifest several hours later."

"You mean weeks."

"No. I mean hours."

"But that can't be," he says, almost laughing. "It's impossible. Isn't it?"

"I have a hypothesis about the incubation cycle at this point," she tells him.

"But it's preposterous! If the disease is closely related to rabies and is a latent feature of HK Lyssa, then one would expect a period between exposure and becoming symptomatic to be more like its rabies cousin-anywhere from twenty to sixty days." He blinks. "Wait-what is your hypothesis?"

"I believe the disease may have been bioengineered and that is why it is so efficient."

Hardy breaks into a sweat. "Oh, Jesus. A terrorist weapon?"

"I do not know, obviously. But that is not important right now. What is important is given the aggressive mode of transmission and the lack of immunity in the population-even those who have caught Lyssa and recovered-the disease has a transmission factor that is likely equal to or greater than R2."

"Exponential spread. Of a disease that is transmitted through aggressive biting."

"It's almost impossible to confirm without field data," Petrova says.

"And then there's the incubation period of several hours."

"Yes. As I was saying to you, the implications of my findings are naturally quite significant."

"You can say that again," Hardy snorts.

"I would like to speak to some epidemiologists to discuss with them what they are learning in the field. Meanwhile, we will need to s.h.i.+ft resources from curing the version of the disease transmitted by sneezes to the version transmitted by bites. Obviously."

Hardy rubs his hand over his stubbled face, staring over her shoulder in a daze. "I mean, you're kind of talking about the end of the world."

"You know my background. Ten years working with viruses like Ebola, Marburg, La.s.sa Fever. I am hardly an alarmist. I am only interested in facts. And the facts tell us that the Mad Dog strain is now taking over from its descendant because its victims are now spreading exponentially in the population. That is the disease we need to cure."

The blood suddenly drains from Hardy's face.

"Oh, G.o.d," he says, remembering. "Amy!"

Taking out his cell phone, he hurriedly punches a phone number. "Yes! It's ringing," he says, pacing nervously. "Come on, come on. Pick up the phone." He suddenly feels an irrational rage at his daughter for making him worry. "I got her voicemail." His tone suddenly changes, becoming calm and smooth, a father's voice. "Hey honey, it's Dad. Just calling to make sure you're okay. Give me a shout when you get a minute, all right? I love you."

Outside the Inst.i.tute, the country is falling apart because of the epidemic. Nearly twenty percent of the country's workforce is sick, consuming resources and producing nothing. And the numbers keep growing while supplies keep dwindling. Food and gas are being rationed, world trade has ground to a halt, the economy is cras.h.i.+ng, and prices for everything from cigarettes to toilet paper are skyrocketing. Most states have declared martial law under the Emergency Powers Health Act.

On the radio, preachers are saying it's the Apocalypse.

But now this. Well, Hardy thinks, if Petrova is right, then it won't just feel like the end of the world. It really might be the end of the world. Infection will spread exponentially until everybody gets it except for those smart and supplied well enough to stay hidden for the next few weeks. Billions will die. The survivors, many driven mad by what they have seen, will live the rest of their days scavenging among the toxic ruins.

If she is right, the stakes in the race for a cure, already high, have just been raised to the ultimate level of a fight against possible extinction.

After hanging up, he glares at Petrova. "You're making me worry."

"I am simply the messenger," she says, staring wistfully at the phone in his hand. He can tell she is thinking about her family and wishes she had a little time so that she could try them again in London. He feels ashamed by this.

"Okay," he says. "Show me your test results. Let's hope you're wrong."

Then he freezes in his tracks and smacks himself in the forehead.

"Dr. Baird!" he shouts.

And rushes out of the room.

Puppets

Hardy jogs down the hall trailed by Petrova, his heart pounding in his chest. He just remembered that Dr. Gavin Baird entered the Inst.i.tute last night shouting for help. On his way home, he got caught in a small riot of cops and looters outside a supermarket, and a child bit him on the hand, breaking the skin and drawing blood. Shaken, he returned to the Inst.i.tute for antiseptic and a bandage minutes before the tall blonde and her mob showed up. Like the other scientists, he eventually gave up waiting and went back to work, disappearing into Laboratory West with Marsha Fuentes, one of the lab techs.

Hardy has not heard from either of them since.

Lucas leans out of his office, adjusting his gla.s.ses. "Do you know where the trash bags are kept?"

"Come with me!" Hardy roars.

"Should I come, too?" Saunders asks, then falls in with the rest. "Why aren't you wearing your mask, Dr. Hardy? Are you lifting the self-quarantine regime?"

Hardy pauses at the door of the lab, looking through the porthole but seeing n.o.body inside. "Has anybody seen Marsha since yesterday? Marsha Fuentes?"

The others glance at each other and shake their heads.

Hardy looks into Petrova's eyes wearing a sad expression. Then he opens the door and steps inside, holding the putter defensively.

Marsha Fuentes walks towards him from across the room, whimpering. What is left of her, anyway.

She has been beaten black and blue. The left side of her face is purple and her eye is swollen shut. Her arm appears broken and, perversely, one of her b.r.e.a.s.t.s is completely exposed through a tear in her s.h.i.+rt and bra. She winces with each step.

"G.o.d, Marsha, are you all right?" he says, taking a step forward.

"She is one of them, Doctor," Petrova says.

He realizes that Petrova is right: The woman's throat is swollen, as if she swallowed crabapples that are now lodged in her throat. She's growling, making the buboes vibrate.

"Aw, Marsha," he says sadly.

"What's this all about?" Lucas says, sounding panicked.

"Christ, what is that smell?" Saunders says. "What was she working on in here?"

Baird went Mad Dog and beat the c.r.a.p out of Fuentes. He also bit her. By the time she regained consciousness, she was already one of them.

Fuentes grins, leaking foam between clenched teeth.

"Maybe we should leave now," Saunders says, blinking.

"Where's Dr. Baird?" Hardy says. "We need to confirm that he's here and then we can get out and seal the room."

He turns to the right and sees the man several yards away, behind a desk.

"Jesus, Baird, you scared the c.r.a.p out of me," Hardy says, forgetting for an instant what his colleague has become.

Baird is growling. His ponytail has worked loose and his long blond hair, clotted with blood, is splayed across his face and shoulders. He's a strong man, a weight lifter. His hands clench into fists.

Hardy can see his eyes through the veil of hair, burning like coals. "Oh, s.h.i.+t," he says.

Baird launches across the desk, scattering papers and sending a PC cras.h.i.+ng to the floor. He brushes aside the golf club that Hardy feebly raises to defend himself, seizes the back of the man's neck and sinks his teeth into his throat. Fuentes, her mouth foaming, latches onto Hardy's left arm and together, the infected scientists bear him to the floor screaming.

"Do something!" Lucas wails. "Somebody do something!"

Saunders shouts repeatedly, too terrified to make words.

Baird has ripped Hardy's throat out with his teeth. A fountain of bright red blood flies into the air. Hardy's scream becomes a gargle. His eyes are gla.s.sy with fear and understanding.

"Mom," he croaks.

Within moments, the lights in his eyes fade. His body relaxes.

The cell phone in the pocket of his lab coat spills onto the floor and begins ringing.

Petrova picks up the golf club and brings it down across Baird's back, making him flinch and yelp like a dog kicked in the ribs. She brings it down again, connecting with Fuentes' broken arm. She rolls on the floor, weeping with agony.

"Get out!" she says, wildly slas.h.i.+ng at Baird again. "Lucas, Saunders, get out now!"

Despite the repeated blows, Baird is slowly rising to his feet, bleeding and snarling, while Fuentes is working her way back across the floor towards her on her knees, holding out her good hand in a splayed claw.

"Get out!"

Suddenly, she realizes that she is alone and that Baird is on his feet. She backs up through the open door and hurls it shut.

A moment later, Baird's body slams against it and begins thras.h.i.+ng and clawing, leaving b.l.o.o.d.y prints on the porthole.

Inches away, on the other side, Petrova sits on the floor hugging her knees and crying, feeling the vibrations and frenzied pounding against her back.

Saunders and Lucas sit against the wall on either side of her, dazed and shaking from an excess of adrenaline.

Suddenly, Baird stops. The silence is startling.

Hardy's cell begins ringing again.

"He's dead," Lucas says, his teeth chattering. "He's dead, right?"

"They all are," Petrova says, wiping the tears from her face.

Gregory Baird and Marsha Fuentes died the moment the virus replicated enough to saturate their brains and subjugate their will to its own. The moment it began using their bodies as puppets for the sole purpose of violently pa.s.sing itself on to new hosts.

She adds softly, "The Mad Dog strain is a parasite, and it has them now."

Petrova slowly gets to her feet, peers through the porthole, and gasps. Baird is grinning back at her, wheezing and dripping drool onto his bloodied tie and labcoat.

Viruses are the world's oldest form of life, primordial and ancient, and yet this mutant strain is something new, she realizes. It is a new force of nature, unleashed upon the world.

A new life form seeking its rightful place in the pecking order.

Baird and Fuentes are no longer making decisions on their own. They are rabid, acting solely based on the virus' simple program: Attack, overpower and infect.

"Oh," she says, backing up. "Oh my."

"What is it?"

She turns, her eyes gleaming and wild, and screams: "RUN!"

Moments later, the door shatters off of its hinges with a crash and Baird spills into the hallway, howling with pain and rage.