"Hey, you don't think mad scientist-ing is, like, a disease or something, do you?" Rex asks in the middle of their post-morning-spar cool-down calisthenics. "I mean, it's not something you can catch if you hit the books too hard...right?"

Six has no idea where this is coming from. That's not especially new. He suspects the effects of long-term active nanite exposure on the human brain, though Holiday claims that teenagers are natural masters of the art of the non sequitur, regardless of their nanite count. Six doesn't recall being so abstract during his adolescence, however. So yeah, probably the nanites. "Not to my knowledge."

"Because," Rex continues, scratching his head uncertainly, "Dr. Holiday's been kind of distracted lately."

"She's under a lot of strain," Six says. Leaving Providence and setting up their own base of operations has been hard on all of them, but Holiday has been responsible for getting all their new equipment in order, and without the cadre of Providence lab techs she used to have. To Six's knowledge she hasn't slept a full night in the last eight months. (A few of those nights might have been his fault. Not as many as he'd like.)

"I know she's stressed out," Rex says. "But lately—yesterday she was late to our appointment in the zoo, I had to remind her. And she almost tried to take an EVO blood sample using her ballpoint pen. And then she poured herself coffee and forgot to put any sugar in it—and then she drank it anyway. Making this face," and he scrunches up his nose to demonstrate.

"Is that all?" Six asks.

"It's Holiday," Rex says. "But she's acting like—like she's changed brains with César." He sits up straighter, eyes widening in alarm. "Oh man—you don't think she actually did, do you? Can that really happen?"

With César Salazar, probably, Six thinks. But he's pretty sure he would notice. And it's not that damning a list, even added to his own observations. Only in the past three days has he observed anything himself, and it's all been small details. Wrinkles in her uniform, a strand of hair escaping her usual neat bun. Holiday at her computer, hastily flailing at the console when he entered, to hide how she'd been staring at a blank screen. And she neglected to come to monitor Rex during this last practice.

And Rex's instincts are solid; it would be stupid to ignore them.

Plus, the coffee. César doesn't drink his black, does he? Yes, they better pursue this now.

Holiday gets up hurriedly when they both enter her makeshift lab together. "Yes? Are you all right? Oh, you just had an exercise, didn't you—did one of you get hurt?"

Six arches an eyebrow at this uncharacteristically flustered anxiety. "No, we're fine, Doc," Rex says. "We just came to—uh—" and he looks helplessly to Six.

"We were wondering if something was bothering you," Six says. "Is anything wrong?"

"Yeah, what he said!"

"What, me? No, nothing's wrong," Holiday says, essaying a smile. She's telling the truth, but the smile's a lie. Interesting.

"Are you sure?" Rex presses. "You've seemed kind of out of it, lately. And Six was saying you've just been stressed—"

"Did he," Holiday says, arching an eyebrow of her own that relievingly disproves the César mind-switch hypothesis.

"—but we're always stressed, with saving the world and everything, so if there's something else—"

"If Agent Six has noticed my stress levels," Holiday says, as arch as her eyebrow, "then maybe he could do something to relieve them."

She looks at Six pointedly. Rex looks from her to Six and back again, frowning, then straightens up with an audible Oh of understanding and turns on Six. "Six! Did you forget something? Like maybe your six month anniversary?"

"No, I—" Six starts to deny, then stops at Holiday's expression over Rex's shoulder. She's not a woman to beg, but her eyes are pleading. He acquiesces, "I may have. Dr. Holiday, will you let me make it up to you with dinner tonight?"

"That would be lovely," Holiday says, and Rex grins at this averted crisis, as proud as when he's successfully cured an EVO.

Entirely missing that a floundering romance isn't the crisis. Six is very curious what is. It's not Holiday's style to play Rex like that. He's looking forward to dinner, and not just because he'll be sharing it with the most beautiful and brilliant woman he knows.

o o o

They haven't been established in their new location long enough to know any restaurants in the area that are above take-out. Instead Six flies them out to one of his old favorites, the Szechuan place in downtown Portland. It's pricey enough to be above the average Providence agent's paygrade, and has the advantage of putting a good hundred miles between them and the dam base.

Still, Holiday cases the restaurant as they're seated, atypically nervously and unprofessional. She fiddles with her napkin as she glances around, too overtly, not just from table to table but the windows, the ceiling skylight.

To put her at her ease Six offers, "Rex isn't here."

Holiday's darting eyes return to him. She doesn't try to deny it, just says, "He's not? You're sure?"

"I'm sure," Six says. The kid is skilled, but not that skilled. Six trained him in covert ops; even if Six doesn't himself remember most of those lessons, he still knows every surveillance trick in Rex's book.

Besides, this afternoon Six took the precaution of getting on Rex's game system and topping the highest scores the kid's ever set in Tiger Beatdown. That should keep him busy for the evening.

Holiday looks relieved, and then, if Six reads her right, guilty about her relief. "It's not that I...but this...I don't want..."

Six nods his understanding. All things considered, Rex is a damn good kid—or forget the faint praise, a damn good man. But he's still a teenage boy, naive in some areas, for all he knows more than most adults about the important things.

"So what is it?" he asks, not bothering to specify that Holiday isn't obliged to answer—she knows that; if it's none of his business she'll tell him so.

But she doesn't; instead she says, "Later—can it wait until after we eat?"

"Of course," Six says, and motions for the waiter.

As they wait for their food, Holiday makes small talk, asking about Rex's progress in his new combined build combat techniques. Six obliges with what answers he can, considering she's observed most of that training herself and knows the exact parameters of his technical aptitudes better than Six anyway. He asks her about her sister instead, and Beverly's new college career gets them through the appetizers to the entrees.

Rebecca picks at her rice and pork, eats slowly as if to make it last longer, even though she seems to have little appetite. Distracted, like Rex said—except no, that's not it exactly. She's watching every bite she picks up with the chopsticks and puts her mouth. Not preoccupied with a conundrum, lost in thought; it's more like she's focusing on the simple task of eating to distract herself from her thoughts. Hiding from a problem? But that's not Holiday's style.

He's not trying to be discreet, but it still takes her until halfway through dinner to notice his attention. "What are you looking at? Do I have something on my face?"

"I wouldn't know," Six tells her, "I'd have to stop looking at your face to tell."

Holiday blushes slightly, to his satisfaction, but doesn't lose the introspective look. Six orders dessert to spare her, but she doesn't accept the mercy. Once the waiter has presented their fried buns and unobtrusively slipped away (he's an expert at inconspicuous, one of the reasons Six likes this place, though he's yet to successfully deduced what renzhe master the staff trained under), Holiday takes a sip of water, puts down her glass and breathes one deep breath and says, "Six."

Then she shakes her head. "Six—I can't—what's your real name? It seems...inappropriate, to be sleeping with a man whose real name I've never even heard..."

Six raises an eyebrow behind his sunglasses. He would have expected the question of such impropriety to have come up before this. If it really mattered, that is. "Six is my legal name." In some countries, anyway, and such as he has a legal existence at all anywhere.

"No, I mean..." Holiday puts her hands to her head, rubs her temples like she's getting a headache. Looking down, so she doesn't meet Six's eyes. "What's the name on your birth certificate?"

"I don't have one." Not anymore, anyway; not for a long time.

"But what do—you can't always just go by—that's a number, not an identity; it's ridiculous to—"

"Rebecca," Six says.

She lowers her hands, looks up at him. "Sorry," she says. "I'm sorry, it's fine. It's just..."

Six puts his hand on the table, beside the plate of untouched buns. After a moment Holiday reaches out to put her hand in his, and Six clasps her fingers, delicate and strong at once. Her hand is steady, no trembling. Still Holiday, definitely. "Tell me," he says. Not an order but a request. A supplication. I can't help unless you tell me. He doesn't need to say that; she knows why.

She nods, and tells him.

o o o

The floodgates, opened, drown him in science at first, a torrent of technobabble, Holiday talking fast and furious about regression experiments and energy potentials. Six nods and rides the waves, not trying to understand. He's not a scientist, but Holiday is; she needs to say her ideas aloud to clarify them, confirm them. Publication, if not in any journal.

She barely notices when he pays for dinner and they exit outside, caught up in her account. But she stops him with a hand on his arm as he steers them toward the waiting jump-jet. "No, it's a nice night, let's stay outside. How about there?" and she indicates the small city park on the corner, half in black shadows under the trees.

The only evident tech in the park is the streetlights, and those are all old electric, pre-nanite. And still Holiday goes quiet as they stroll past the open gate, peering into the shadows. With Six she has no reason to worry about muggers, and she knows the unlikeliness of an unreported EVO in a city's downtown.

Excepting one particular EVO, of course. "Rex still isn't here," Six says.

"Yes," Holiday says. "Okay." She whirls around on the paved path, suddenly enough that Six tenses, scanning the darkness for a threat—but Holiday just points a finger at him. "You can't tell him—you understand that, right? None of this, you can't breathe a word of it to Rex."

"I won't tell him," Six says.

"Or White," Holiday says. "I haven't said anything, haven't talked to him, he doesn't—he hopefully doesn't have an inkling. If he knew—if he even suspected—you can't tell him anything, you can't."

"I won't."

Holiday nods, not content, as uneasy as before.

After a moment Six asks, "What am I not telling them?"

"Oh," Holiday says. "Right." She shuts her eyes as if concentrating all her will on taking her next breath, opens them again and looks up at him. "Were you listening to any of what I was ranting about? If any of it made sense—I haven't had a chance to put it in order. Didn't dare type any of it up, had to keep it all in my head, and I couldn't tell anyone, of course..." That's the source of the strain as much as anything, to have drawn a black-out curtain over her brilliance, the pain of a teacher denying themselves the chance to teach.

"I was listening," Six says. "I didn't follow all of it." Or most. Or any. Something to do with nanites. After that he's at sea.

"Right," Holiday says again. "Okay. You know we took some experimental equipment with us, prototypes—failed, most of them, or incomplete. Things Providence wouldn't miss."

Six nods.

"I tried to keep up with all the current research projects, but I didn't have a hand in all of them," Holiday says. "And some are from before my time. I copied over most of the documentation before Black Knight froze my login, but some of the notes are haphazard at best. Researchers scribbling down their brainstorms and then never bothering to do complete write-ups, when their avenues of investigation failed. And they mostly do fail. Scientific progress is the ongoing ordeal of throwing ideas at a wall until finally a brick in the wall breaks instead of the hypothesis..."

Six nods again, letting her speak, order herself. Find her way through the intricacies of her genius back to him.

"So one of these experiments—several of them—you remember Dr. Fell? —Or, not remember," she corrects, sensitive as always to what he's still missing, "but do you know about him?"

Fell had been the first director of Providence's research department. Six has seen the employee ID pictures, tall, gray-haired, nothing special. But looking at the images always makes his hands curl into fists; Six has to fight the urge now. He'd had to do some digging to figure out why. The footage from the labs, the experiments—Rex, younger and smaller, strapped to the not-so-good doctor's table. "I know about him."

"His methods were abhorrent," Holiday says, "and personally I—well, never mind. Ancient history. But he was brilliant. Some of the analysis equipment we have now wouldn't exist without his work. When Fell...left"—was fired, and Holiday replaced him, a vast improvement by any measure—"he left multiple projects unfinished. Some were picked up later by other researchers, in and out of Providence; others were left by the wayside, forgotten.

"One of these—well, several, but one in particular—is in our database. I discovered it a few months ago, have been looking it over in my spare time. Fell was—not close, but he was on the right track, maybe. He didn't think so, but knowing what I know now, especially with the Omega nanite—I'm almost positive, if the synchronization were complete—it would be possible. It would almost definitely be possible."

"What would be possible?"

"The cure," Holiday says. "The final cure, for everything—complete deactivation of all nanites, globally. Instantly—or as long as it would take the signal to propagate, so the speed of electromagnetic transmission. Instant from the human perspective, if not the electronic."

Six reminds himself that breathing is an important function. In Cambodia he once held his breath underwater for four minutes thirty-six seconds, but that was years ago and his lungs now aren't quite up to that capacity. He makes himself inhale, says, "You've found the cure?"

Holiday opens her mouth, closes it. Opens it again. "I—and Fell's research...the theory's solid. Preliminary tests support it."

"That's." Six searches his memory to no avail. Maybe he learned the word he needs now in the past six years he lost. He settles on, "Amazing."

"No," Holiday says. In the park's shadows she's pale, her face white against the darkness. "No, it isn't. To do it—to accomplish the complete shut-down—the Omega nanite could be used to synchronize a local internal signal with the rest of the nanite population. It would only be a temporary hack; I doubt we could manage it more than once, for just a brief window. But during those minutes, if the local nanite set was deactivated, then the rest of the world's would follow suit."

"So, cure one, and everybody else is cured?"

"Not...exactly," Holiday says. "The goal isn't the ordinary return to the passive state, but a complete shut-down. It's the only way to stop those incurable nanites that won't respond to the standard deactivation commands. Normally there wouldn't be any way to initiate such a shut-down—the nanites are programmed to go inactive, but they reset when they enter a new host, by design.

"But there is one unique set of nanite code that does include a final shut-down protocol, under specific circumstances. One set designed not to seek secondary hosts, but to turn off—a soft self-destruct, really, deliberately shorting the internal circuitry—upon the cessation of the original host's biologic function."

Six is intimately familiar with all the myriad ways to state that particular concept. Holiday's scientific prolixity is far from the most coldly rational he's heard. "So when this original host dies—"

"His nanites go out with him," Holiday confirms. "And, if they were properly synched up, so do all the others, around the world."

And the planet is freed of its plague. Holiday is declared a hero, awarded every scientific prize on the record; probably they'd invent another couple Nobels to give her. Humans can get back to the important business of finding whole new ways to kill each other and end the world. Life goes on, et cetera, et cetera.

Except for the poor bastard unlucky enough to have hosted those specific, unique nanites with the shut-down code.

Holiday's face is bone-white, corpse-white, through the shadows. It still takes Six a couple of seconds to get it. Denial, he recognizes.

"Rex," he says. His lips are numb. "You're talking about Rex's nanites."

Holiday crosses her arms over her chest, tightly, as if to hold in her heart. Wordlessly she nods.

Rex's so very specific nanites, with their so very unique code, the source of everything he does that no one else can do. Programmed to have him as a host and him alone, accept no substitutions. If those nanites were synched up with the rest of the world's, then all he would have to do—and then if he—if Rex—

Six has witnessed, caused, presided over more deaths than can quickly be counted—more than he remembers, if not by choice; by choice he remembers all of them, accepts them all for what they have made him. Allies and enemies, foes and friends and family.

But this, this one, this death, he cannot imagine. Not even that he can't bring himself to do so. There's nothing there when he tries. More blank than the six years taken from him—he still has fragments, impressions, dreams, as well as all the records and other people's recollections, from that lost time. For this, there is nothing.

"You can't tell him," Holiday says, meeting his eyes through his shades. "Rex—you can never tell him."

Of course the kid can't be told—he trusts them now, but if he knew the truth—knew that the cure they'd sought for so long, struggled and studied and bled for, hinged on him—

If Rex learned that saving the world would cost him his life—if he knew that he was the key, that all it would take was his sacrifice—

A damn good man, for all he's still a boy. And a true hero, in every sense. He'd believe in Holiday, would trust her research. Trust Six's faith in it. It wouldn't be what he wanted, not his first choice, and he'd argue and protest and rail against the unfairness. But when it came down to the wire, with the world in the balance, he'd submit to it. Volunteer for it. Hell, demand it. To save the world, Rex would accept his fate of his own free will, eyes open and heart pure.

No, they can never tell Rex.

Nor White; that goes without saying. For this end, any means would be justified. Six cuts to the chase. "Have you deleted the original research notes yet?"

"No," Holiday says, "I've got them encrypted, but—"

"White monitors the whole system. Encryption won't shield them from him forever."

"Yes, but..." Holiday shakes her head. "I was hoping—if I continue studying it—there might be another way, a different option further down the line. If there were another method to produce the shut-down signal—a harmless method—"

"Have you thought of any?"

"Not yet, but Six, I can't think of everything! If I pursue the research bring some more scientists into it...César, for instance, he might have some thoughts..."

And from César to the Black Knight, inevitably. César might see his brother over the solution—or maybe not; Six doesn't fathom how César's vision works, and never would want to. But Black Knight, like White, would see Providence's cure, first over all.

Holiday knows this already, or she would have contacted César before. She trails off, turning away from Six to look into the park's darkness. Says finally, "We can't risk it, can we."

In the time they've been talking, his eyes have adjusted; he can see between the trees to the surrounding buildings. Nothing hiding in these shadows. The only monsters here are those they've brought themselves, those they carry with them. More invisible than their nanites, and more terrible.

"No, we can't," Six says. His measured certainty is a warning as much as anything; if she doesn't erase the data, he will.

Holiday knows he would. It won't come to that; she's too responsible to leave this to someone else, not when it's her discovery.

Still, it takes a long moment before she sighs, a long whispered breath, as if she's exhaling more than air, letting go of something. Hope, maybe. Or else fear. "All right," she says. "When we get back, I'll delete them. Run a reformat—the drives have been needing a clean-up after the last virus attack, that'll be good cover. And I'll code a worm to take care of the copies in Providence's system, if you can break into an access point to upload it."

Six nods agreement, then inclines his head at her. "Back to the jump-jet?" he suggests, offering his arm.

Holiday slips her own through his, steady as always; all that betrays her is how her fingers briefly clutch at his sleeve, before she forces them to unclench. They walk in silence until they reach the park's gate. Then she stops, looking up at him through the shadows. "Six," she asks quietly, "is this right? I keep thinking of my sister, how much harder this decision would be, if Beverly were still... Are we doing the right thing?"

He could tell her the truth. How a cure is still hoped and prayed for, from Providence or the other Providence or anyone else, but is not expected anymore, after this long. How it is accepted that some moral costs are too much to stomach. How many people would repudiate a solution that required the life of a child, an orphaned teenage boy.

But Holiday wouldn't be asking him if it was absolution she wanted.

"No," Six says. "It's as selfish a thing as any I've ever done in my life. Maybe more."

Holiday doesn't flinch, of course. Meets his eyes and says, "Then how can we—for the world, to save the world—how can we justify, even to ourselves—"

"You can't save the world," Six tells her. "Not everyone's, no matter how hard you try or how smart you are. Everyone lives in their own world, what they've seen, what they know. Seven billion worlds, and every one of them is the most important of all, to the one person living in it. In the end, that's all you can ever save. The bravest and most self-sacrificing hero's altruism is ultimately still the selfish wish for their world to go on, even without them in it.

"This cure would save the world for a lot of people. Maybe almost all of them. But your world, my world—they would end when his life did.

"So yes, it's selfish, and no, it isn't right. But it's what we're going to do." He wouldn't presume to speak for her, usually. But he knows her heart matches his own in this.

"And Rex can never know," Holiday says. They both know that, too, that what they can live with, he could not; too young and too naive, too empathetic and too heroic.

Someday, when Rex is older, when he has a family of his own, he might be able to understand; or maybe he won't, too great a hero to accept the loss of lives he might have saved. Either way, they will bear this for him. Holiday has the strength. And Six will find it, if he doesn't have it yet, for the sake of the man he's supposed to be.

The jump-jet's cockpit isn't designed with companionship in mind. But back at the base, Six gives Holiday a hand climbing out, and their hands stay clasped as they walk back to her lab. It's such an innocent gesture that the intimacy of it surprises Six. Before it can become too uncomfortably close, he leans in to kiss her, re-establish the usual parameters of their relationship.

Of course this is exactly when the lab door opens and Rex tumbles out, going, "Hey, you're back. How was the da—ack! Um! Sorry!" and he attempts a strategic withdrawal so fast that he backs into the doorframe instead of the doorway, mutters an "Ow!" when he thwacks his head on the jamb.

Six raises an eyebrow to draw attention away from his uncontrollably quirking lips. Holiday smiles more kindly, says, "We had a nice dinner, thank you, Rex. Now, Six and I have...important business to take care of, so if you would excuse us..."

"Yes, right! Of course! Excusing away—excuse me!" Rex feels along the wall to correct his course as he backs away from the lab, ushering them inside while grinning like an idiot. As they enter he waves a good night to Holiday and gives Six possibly the world's most ill-concealed thumbs' up before closing the door on them.

Holiday smiles slightly, murmurs, "Well, we weren't lying about the business, but I think he might have gotten the wrong idea..."

Six raises his other eyebrow at her, suggestively. "Or the right one." It's not that late, and reformatting the drives will mean most of the system will have to be off-line anyway—and she shouldn't have any other plans to fill the downtime.

Holiday nods, but the look in her eyes is abstract, not salacious. "First, however..."

Before she can access the computer, they hear a thud in the hallway, followed by a shout of, "Bobo! No, don't put that—" followed in turn by the crash of something shattering.

There's a moment of expectant silence, then a knock on the door. Rex calls through it, "Don't worry, it's no problem, I'll take care of it—you guys just get down—to your business—to the business! That's what I meant!"

Holiday looks at Six as Six looks at Holiday.

"He probably can handle it," Holiday says.

"Probably," Six agrees.

"And that probably wasn't my primary EVO sample collection tray getting dropped on a concrete floor."

"Probably not."

Holiday shakes her head, gets up from the terminal. "First...I better go make sure." She sighs with long-suffering patience, but it's not entirely convincing, when the disquiet in her eyes has been replaced with dancing laughter.

When she comes back, Six knows, there will no hesitation, no last-minute reprieves as she consigns years of research and genius insight back to the limbo of the unknown and unconceived, along with all their possibilities. All the worlds that could be saved; all the lives that might now end, that maybe wouldn't have.

And one life that won't end, that would have.

Not an easy choice; not the right one. Not the choice a true hero would make. But he and Holiday are not the heroes of the world, and this is the only choice that they could live or die with, the only one that they would ever make.

the end