[Author's note: I will not even try to explain why it actually took me more than six years for this seventh installment. I really hope some of you are still checking in and are ready and willing to give the story another chance. It will definitely go on from here and will be finished - maybe not as smoothly as I would wish to, but I will give my best. Also my heartfelt gratitude to my wonderful beta who picked up her great work on "Lex Tertia" as if nothing had happened at all. Thank you!
You may recall that a central theme of "Lex Tertia" is a raging pandemic of pneumonic plague. In the face of COVID-19, it took me a few weeks after chapter six was finished to decide whether or not I should update at all. As you see it's here now - and I can fully understand when you don't feel like dealing with that particular topic right now. Maybe you'll be able to come back later. I'd be thrilled and grateful.]

Chapter 6

Leaning back in his lab chair, Spock allowed himself the tiniest of sighs. A strange mix of unfamiliar emotions, heavy on frustration, had been nagging at him for the better part of the morning, and there was no indication that things would improve any time soon.

Their so far only approach to contain the pathogen had looked very promising. It had been triggered by his decision to finally tell Khan about Dr. McCoy's attempt to slow down the infection in his crew mate. Spock had not been naïve enough to expect any gratitude for the doctor's efforts (and he received none) but Kahn had been immediately inspired by McCoy's method. As a result, they had spent the following four five days determining whether extreme reduction of in-vivo temperature might prevent Yersinia from developing its protective capsule. The idea had been as elegant as it was had been encouraging, and Khan's theory that with a diminished capsule, at least one of the newly developed antibiotics might finally take hold, had evoked a degree of optimism Spock had not experienced in weeks.

There had been no concept as to how applying to apply the method, should it have proven successful, to the millions struggling for their lives all over the planet. Yet it would have been a substantial step forward and Spock was painfully aware of the crucial relevance of any breakthrough whatsoever.

As well as of the fact that Khan's latest brainchild had been born from anything but altruism.

However differently their mutual hopes might have been motivated, though, they had been effectively crushed during the night before which Khan had spent evaluating their latest and decisive test series. Just half an hour ago, right after Spock had entered the lab this morning, Khan had informed him about the Yersinia colonies that had undergone cold treatment were thriving in their blood agar dishes. None of the newly developed antibiotics had made any impact whatsoeverimpact.

And the morning took a turn for the worse when Spock had related the very grievous news of his own. Three hours ago, Khan's man had been reported to show the first symptoms of pneumonic plague.

Spock had found delivering that particular information unexpectedly…difficult, but had deliberately refused pondering the reasons for that. Instead, he had been completely focused on the man on the other side of the lab table. Profoundly aware of the craving for revenge Khan was harboring, Spock watched closely for any sign of that most effective, single-minded violence.

He had been prepared for a wide range of reactions. The absolute lack of any perceptible response he got had gottenhad received had not been one of them. Khan's pale eyes had simply, steadily held his during the short report about the onset of fever, shivering attacks and accelerated breathing. After the final words of his report (because this was exactly what it had felt like) had faded into silence, Khan had regarded him for one more intense moment before wordlessly turning back to his data station. Where he had been working ever since.

Spock could literally sense them. The fine fissures creeping through the fragile truce they had reached during the past weeks, ruthlessly extending with every minute that passed. They were losing their shaky common ground, the foundation that was essential for success, and they were losing it fast. Spock knew this was a process that had to be stopped, just as he knew that since it had been his news to rip the first crack, it was also up to him to mend it. Not sure at all if he had the means to do so, he was positive that ending the leaden silence that had fallen between them was the first necessary step.

And after that, it would also depend on Khan if and where they would go on from there.

"The diminution of the pathogen's ambient temperature might be an option that could actually lead to success if carefully refined." His words seemed to drop to the floor, bursting there like glass.

"The fact that this concept was the most promising so far easily tempts to pointlessly cling to it." Khan's answer came without the least delay, his voice low, his gaze glued to the screen in front of him. "Do not make that mistake. We need to accept this approach as the dead end it is and move on."

The almost physical alleviation of tension Spock experienced at Kahn's obvious willingness to bridge the rift clashed with his dismay at the other's clear dismissal of their work of the past days. He himself was very reluctant to abandon the concept without exploiting it to its full extent. That was the reason, of course, why he could not restrain himself from disagreeing. And not the tiny spark of resentment yet another lecture about the rules of scientific work had triggered, however gently (considering Khan's standards) it might have been delivered.

"There might be the possibility that we have not yet exhausted the full potential of this approach and therefore…"

"There *is* no potential, Mr. Spock." Khan cut him off with a little more force behind his words than before. "Reducing the ambient temperature obviously and expectedly merely slowed down the pathogen's activity. Regarding the prolonged incubation period in my crew mate, it might even decelerate the infection. That is all there is to it."

"I cannot relate to that point of view. And I would think that regarding the current condition of your man, you should also…"

Khan's hand slammed down on the table beside his data unit with a forceful crash. Unable to suppress a slight wince at the sudden sound, Spock found himself effectively interrupted.

"You better put up with the fact that the only thing we've achieved is excluding yet another option for action. Essentially, Yersinia's pathogenic properties remained entirely unaffected. Face it, Mr. Spock." His physical outburst notwithstanding, Khan's words had been devoid of any emotion. When he lifted his head, though, his gaze was glacial. "And you need not to worry. It is not to be feared that I might forget about the condition of my man."

Understanding hit Spock the instant Kahn turned back to the data screen. So he himself had done it, too. Had fallen back upon using Khan's crewmate to force through his belief of the best course of action.

"I sincerely apologize for…"

It was as far as he got.

"Don't." Khan rose from his seat, histhose eyes as cold as before. "Interrupting our work in order to placate each other every time we've not been able to hold back our mutual contempt will only result in an unforgivable waste of energy and time. We both know that neither of us wants to be here, yet we are because your Federation had to resort to the help of a man from the second half of the twentieth century they'd actually rather…"

He was half-Vulcan, so he did not miss it. The subtle change that rippled over Kahn's face. The slight widening of his eyes. The lips that remained parted, just the tiniest bit, after he had suddenly fallen silent. Probably because when it came to Kahn, those miniscule signs amounted to an emotional outburst, Spock actually interpreted them correctly.

So when Khan's gaze gradually came back into focus again and drilled into his, the bright light gleaming in it lifted Spock's heart in most irrational, most human, most reflexive hope.

Purpose.

Certainty.

Usually the background of his entire existence.

He wasn't used to the complete lack of both. Yet, ever since he had been forced into this… cooperation with the Vulcan, the sense of certainty had dwindled with every approach to the problem he'd had to eliminate. Until even he himself had begun to doubt. Seriously. So for a while now, he had been running on purpose only, but when he had learned about the outbreak of the disease in his man this morning, even that had finally left him.

The sheer despair that remained had been (and yes, he was ready to admit that, if only to himself) downright scary.

Therefore,So when he finally made the connection that would make all the difference, when, after all, his reference to his own origins had triggered this critical brainwavememory of the one name he had needed, the relief had been overwhelming. He knew he had not been able to keep it from showing, and the answering reaction he had seen flaring in the Vulcan's eyes only went to show how transparent he had been that very moment.

He didn't care.

Not in the least.

With the name still fresh in his headmind, Khan kept eye contact with Spock for another fraction of a second. Allowing them both, for no reason at all, to share that particular moment he knew to be the turning point. The sharp intake of breath he heard when he abruptly, wordlessly returned his attention to the data screen, added a certain amount of satisfaction to his renewed confidence. With a small inward smile, Khan waited for the comment to come while his fingers flew over the panel in front of him.

He didn't have to wait long.

"I understand you have arrived at a possible solution."

At any other moment Khan would probably have allowed himself a sliver of a smirk at the obvious confidence put in him by Spock of all people. Right now, though, his entire focus was elsewhere. Knowing how small it was of him, Khan therefore settled for keeping Spock in the dark a little longer with his simple answer. "Yes."

His mind already fully on the task at hand, Spock's wordless indignation on his taciturnity merely scraped Khan's awareness. Usually, he would have blindly trusted his memory, which so far had never failed him. Wasn't built to fail. Yet he was human after all, and as such had impressively proven in the past that he was not immune to making mistakes. Yet, and Ffor the same reason, though, he was also capable of learning from them. So the first step he would take in saving his man was to eliminate uncertainties. He *would* verify. Thoroughly and conclusively.

At the margins of his perception, he was aware of the Vulcan approaching him, registered that he was spoken to. Blocking out all of Spock's attempts to communicate, Khan concentrated on the screen before him, feeding his unit one search command after the other, sifting through layers of centuries of information within moments. When he finally discovered and followed a thin track of data only detectable for those knowing what they were looking for, he was not at all surprised to find that the method, which had not been very popular even at his time, had more or less disappeared ever since. Yet, Khan eventually arrived at its source, noting with no little satisfaction that the name still singing in his mind had been the right one.

Leaning back in his chair, Khan closed his eyes for one moment, yielding to the overwhelming need to mentally and emotionally settle down. Maybe the Vulcan had realized and accepted that necessity, maybe he had resigned himself to the fact that Khan would volunteer information at his own terms only. For several heartbeats, however, utter silence reigned. Until Khan decided to break it.

"You know, Mr. Spock, your Federation had been right after all to look for help from the past in order to save its future." Khan kept his voice perfectly even, not betraying the thirst for action he felt already boiling through him. "They just have not gone back far enough."

"Georgi Eliava?"

Spock caught himself cocking his head, a Vulcan habit when encountering the unknown, and one he had been working on hard to suppress for the better part of the past three years. The name felt absolutely foreign on his tongue, didn't trigger the slightest memory or connection. And Kahn still had to offer more than a cryptic reference to the timeline and that faintly Slavic sounding name.

Raining in a faint whisper of rare annoyance, Spock chose his next words very carefully.

"I am afraid I have never heard neither of that name nor of any scientific achievement attached to it."

Khan's eyes never left his, his words falling between them calmly, perfectly modulated.

"It would have been astounding if you had, Mr. Spock. The man in question lived shortly enough from 1892 to 1937, Christian Era. As a microbiologist, he co-discovered and introduced to medical research the technique we will defeat the recent Yersinia strain with." Spock watched Kahn turning the data unit to allow him a glance at the screen. "Phage therapy, Mr. Spock. Or biocontrol, as it has also been termed."

Spock only realized that he had actually expected to recognize or at least be inspired by the term when neither happened. His cluelessness must have shown, perhaps in another involuntary gesture, because Khan, leaning back in his seat, finally elaborated.

"Phage therapy is a highly specific method of fighting bacterial infections, employing viruses which infect and therefore destroy pathogenic bacteria. Yet the technique of using such bacteriophages never replaced the application of antibiotics except for a few countries in the then still existent Soviet Union. With the discovery of new and more potent antibiotics in the middle of the twenty-first century, though, phage therapy seems to have disappeared from medical awareness altogether. Which explains why your research team has never hit on the idea."

Spock literally felt his brain catching up with the facts he was told. He indeed had never heard of a medical method employing viruses to control bacteria, yet his microbiological knowledge was thorough enough to realize its potential immediately. The confidence he had felt earlier (he would never call it hope) had been replaced by a degree of assurance that bordered on certainty. Yet, he had spotted a rather significant flaw in the strategy, too.

"If this method has only been put to selective use during the twentieth and twenty-first century, after which it apparently was completely eradicated from scientific reality, it will take us a probably too long a time to replicate it, if we succeed at all."

The disturbingly intense gaze Khan threw him charged the small roomair with tension. Spock endured it with an outward stoicism he did not necessarily feel, realizing that his remark had brought up once again the different…well, timeframes they were working within. What might be developed too late to save Khan's man could still be of invaluable help for millions of others. Pondering the minefield this fact turned their conversations into with increasing frequency, Spock watched Kahn getting up from his seat.

"As you know, Mr. Spock, my training included biological warfare, as Admiral Santiago so aptly put it." Khan had started to move through the lab, opening closets and checking the contents of shelves as he went. "I'm not only familiar with the instruments and general methods of micro- and molecular biology of the era in question, but very adept at them as well. "

For once to Spock, the easy arrogance Khan's words were humming with translated into nothing but unwavering confidence. To his ears, at this very moment, nothing could have sounded more promising.

"Would it be correct to assume that you believe to be able to successfully execute Dr. Eliava's method?"

Closing one last drawer, the pale face a study in calm satisfaction, Kahn turned back to him.

"Mr. Spock, I am absolutely positive."

"So he actually did it."

The sound of rain hammering against the windows of Kirk's apartment had been a constant background song to Spock's detailed report of the day. The captain and Dr. McCoy had listened with the usual focus and sobriety marking their recent evenings together. It was only right. The graveness of the situation commanded nothing else.

Not entirely sure whether McCoy's words had been phrased as a question or statement, Spock opted for a careful answer. "It depends on how you would define 'it', doctor." He reached for his so far untouched glass but did not lift it to his mouth. "Khan certainly found the theoretical method. He still has to prove he is also capable of applying it."

McCoy leaned forward in his seat. "But you think he is?"

"It is hardly relevant what I think…"

"For heaven's sake, man!" The sudden outburst drowned out the steady pelting of the rain. "Do you even hear yourself talking? This is probably the one shot we've been looking for, the only one we might get, and you are picking apart semantics! If it wasn't for…"

"Bones." Kirk emphasized his verbal interruption by putting a hand on McyCoy's shoulder, which was shaken off immediately. With a furious glance at Spock, McCoy shoved pushed himself up from his seat and, grabbing his glass, marched to one of the windows where he settled to wordlessly stare into the rain.

Philosophically, Spock finally took a measured sip from his own drink. Situations like this were nothing new; during the first months of their deep space mission, open conflicts between him and Dr. McCoy had been a most regular occurrence. Interestingly enough it had been the captain, not exactly an authority on emotional control himself, who had proven to be a rather capable mediator.

And was, right now, living up to those standards again.

"No one is expecting dubious predictions, Spock." His calm voice a stark contrast to McCoy's yell, Kirk settled back in his seat, probably an attempt at demonstrating ease despite the palpable tension in the room. "Still, it's you who's been dealing with him, working with him and most surely assessing him for almost two weeks now. So I think it's quite natural and *logical* that you are asked for your professional opinion on his abilities. It's nothing more we want from you."

If his human half was, well, chagrined at the well-hidden reproach, the Vulcan part of him easily managed to ignore it. Silencing the small whisper that reminded him of times not so long ago when he would not have been able to brush off the tiny pang of disappointment so effortlessly, Spock carefully put his glass back onto the table.

"Captain, I have only been able to witness Khan's dealings with contemporary methods and instruments so far. The method of phage therapy or biocontrol includes several steps that might appear anachronistic, even archaic to a 23rd century medical microbiologist. There are others that might be hard to accept even by microbiological laymen. I am therefore incapable of judging whether Khan will be able to successfully execute what he theoretically knows."

Kirk's sigh mixed with a small sound from the window, followed by the voice of an obviously slightly calmer McCoy. "But you are sure he fully related this method to you."

"I am, doctor. And, I have to say, it is quite beautiful in the simple way it exploits the basic rules of interaction between bacteria and bacteriophages."

"And aren't you the lucky one to be able to satisfy your need for scientific aesthetics while people drop dead left, right and center." Not screaming this time, McCoy conveyed his fury via perfectly executed sarcasm, which was, of course, completely wasted on Spock. Most likely more than aware of that, his voice picked up a slightly resigned note when he continued. "It is true that I've never heard of a method using viruses as a remedy for bacterial infections. It is also true that theoretically, this is a strategy which could work, even in a human body. But you were the one he presented this to. You heard him. You studied the background data this is based upon. So I'm asking you for your scientific opinion, based upon your own expertise: Does this biocontrol or phage therapy, or whatever you'd like to call it, sound like a feasible option to you?"

Spock took his time to phrase his response. He himself had been instantly convinced of the method. Yet he was also aware that others might not be persuaded so easily – the anachronistic aspects as well as the simple fact that it was Khan suggesting it (ironic, really, since it had been the Federation dragging him and his man into this in the first place) were enough reason for doubt, if not downright suspicion.

"I, personally, regard biocontrol as a most effective and feasible way to finally gain control of the current mutant of Yersinia pestis, doctor. While it may be true that, in light of today's scientific possibilities, the implementation itself doesn't exactly meet the recent state of the art, the microbiological principles it is based upon are indisputable. The requirements might appear to be unusual, but I would like to emphasize that I am more than confident of the prospects of success which, in my opinion, are more than reasonable."

McCoy raised his glass, saluted the room in general, more fatigue than mockery in the gesture. "And I say that's something, after all."

Kirk was still deeply buried in his seat, watching Spock thoughtfully. "How hard was it to convince Santiago?"

Thinking back to the task force meeting, which he had called in immediately after leaving Kahn in the late morning, brought back the heated discussions Spock had endured until just an hour ago. "It was to be expected that Khan's proposal would not simply meet acceptance. In the end, though, nobody could deny the truth of doctor McCoy's words: They are all aware that this could very well be the only option there might be."

Silence fell. And held. It was not hard to tell what each of them was thinking of just then. Another hopeless situation, almost six years ago, just above Earth. Helplessly caught between the planet, its moon and a slowly recovering battleship, poised to destroy them all. And Khan and his help the only chance to get out of it all alive.

Spock knew that right now, the disastrous results of that attempt were on the others' minds as well.

The soft chirping of a communicator ripped through the perfect quiet like an explosion. It took Spock the fraction of a second to realize it was his own.

Flipping the device open, he accepted the call. "Spock here."

At the very same moment, from his sitting position on the cot, Khan watched the change of guards currently taking place outside his cell from under only half- closed eye lids. The Vulcan had insisted he was transferred back here from the lab, alluding, quite pointlessly, to the necessity of sleep or at least some extensive rest. He had complied, not because he actually intended to sleep (aside from the fact that he actually didn't need to yet, he was also very much aware that he would not be able to) but because accommodating that request was an easy opportunity to convey a certain spirit of compromise.

Yet, their goals were very much in line, so lulling the Vulcan into a feeling of safety was not strictly necessary. But seizing his chances to setting the stage as early as possible was most certainly no mistake either.

Especially when the Vulcan's dismay about the outbreak of the disease in his man had been so clearly tangible.

Khan himself had not yet dared to even tap the quivering part within himself where he had bundled up all that had shattered on the devastating news this morning. True, locking it all away was putting additional strain on the iron grip on his emotions, and there had already been too many occasions when that grip had been just about strong enough. But right now, with the solution to the pandemic at his hands, allowing himself the luxury of falling apart (be it with rage, fear or despair) would only do his man a blatant disservice.

The last of the eight guards in front of his cell had been replaced and the senior officer uttered the standard opening statement into the holding unit's log. Khan could have recited the lines along with him, so he didn't pay any attention at all. Except for the mentioned date and time.

He had made a point of being aware of both ever since he had to leave his infected man almost exactly two weeksten days ago now. Time was of the essence. Time could equal life. Or it could equal death. His restless mind counted days and hours, converted them into minutes and seconds. Calculated what he had already lost. Estimated how long he still might have. Set it off against his evaluations of how long it would take him to replicate, to adapt a method last carried through centuries ago.

Arriving at the impracticality of it all over and over again.

Which was simply inacceptable.

Pushing reality to the far back of his mind, Khan settled, again, on mentally going through the first necessary steps he needed to set up as soon as he would be allowed to get started.

He already knew them by heart, each and every stage of the procedure. The six hours since the Vulcan had left for the task force meeting he had called in, Khan had spent with theoretically honing a ridiculously time consuming method into something that, regarding the days he still might have left, *could* savfe his man's life after all. He was aware that his fine-tuning had pushed the feasibility of biocontrol to its limits already. Still it took all of his resolve to not reengineer the individual operations even further, knowing this would result in the loss of accuracy which was vital to the entire approach.

Right now, there was nothing more he could do. And everything he had done so far would not be enough.

Inconceivable!

Somewhere, a door swished open.

Inwardly counting the footfalls approaching his cell, Khan actually did close his eyes for a moment. On the fifth step, he had regained the calmness of mind necessary for finally getting things to work. On the seventh, he slowly got up from his cot. On the tenth, he lifted his gaze to the security barrier.

The Vulcan watched him calmly from the other side.