Disclaimer: I do not own any part of Sherlock; it all belongs to the BBC, Mark Gatiss, Steven Moffat, et al. I write these stories purely for enjoyment; no copyright infringement is intended.

Author's Note: I want to address the wobbly timeline in TSoT the way the episode is structured, it's hard to tell when Sherlock and Mary started planning the wedding, and whether that was before or after John asked Sherlock to be his best man. We know that there were six or eight months between TEH and TSoT, and we know that Sherlock did everything from folding napkins to screening the guests – but he could have done that without, officially, being best man, just because he wanted to make John and Mary happy and give them their perfect day. So, for the purposes of things here, I'm assuming that we are about three months post-TEH, and that while Mary has started wedding planning, John hasn't asked Sherlock to be his best man yet.

Sherlock's quotation is from Alice's Adventures in Wonderland. Somehow I have to believe that even Sherlock can appreciate a children's classic.

Triquetra – Chapter Two

Sherlock thought for a long time after Mary left, slapping three nicotine patches on his arm without any hesitation and trying to make sense of the tumult in his mind.

He found that he was almost paralyzed by the influx of new data; it took over an hour before he could slow his whirling thoughts down enough to make any sense of them, and several more before he had managed to wrestle them into order.

What Mary had told him was . . . unprecedented. Unfathomable. Of all the variables he had considered, all of the possibilities he had agonized over both before his return and after it, the potential for something like this had never crossed his mind. He had been so convinced, when he returned to find John literally on the verge of being engaged, that the best possible course of action was to be as conciliatory toward both John and Mary as possible, to rejoice in their happiness and try to foster it, even if it left him feeling hollow in the moments he was alone. He had been allowed back into John's life, thanks in no small part to Mary, and it seemed the least he could do to help plan their wedding, to be the friend he always should have been.

He and John had left so much undefined and unsaid, had always been at the edge of being more than they were but never quite getting there, and then Sherlock and Mycroft's desperate bid to stop Moriarty had destroyed everything the pair of them had built. Sherlock's tears on the roof of Bart's had been genuine; he had known he was, in all probability, ripping their friendship apart permanently, but even he had not fathomed the depth of the pain and grief that John had endured. It had not occurred to him that he could be mourned so acutely, even though losing John had been like losing the breath in his lungs. Not until he came back, until he had seen with his own eyes that John's loss and desperation had truly been as profound as his own, had he understood the extent of the damage he had done. Ensuring John's happiness with Mary had seemed the only way to make it up to the doctor; Sherlock would never have dared to presume that John returned his feelings. Even before Bart's, John had been absolute concerning his heterosexuality.

Yet today, Mary had said that John had cared, that he had loved. He had realized it too late, perhaps, but John had felt something for Sherlock – and Mary had come to Sherlock with not only her old life held out in her hands, but the potential for a new life as well, one that included both John and herself. Mary Morstan was a fascinating enigma, an extraordinary combination of qualities that scuttled Sherlock's predictions and probabilities beyond the reach of any logical data set. She was warm and full of light but also cold and deadly when necessary, so much like his John.

His John.

No – God, no, he couldn't think about that yet. There was far too much that needed to be resolved before he could honestly hold on to that possibility. He refused to allow himself to go through his memories of John, to see how they had changed now, given his new data. He could not permit himself that until he was sure, until he knew there was a reason to hope. He could not bear to look at memories of John loving him and see only what he had lost, and not what he might have again.

Mary, then. Mary, who was apparently so much more than she seemed on the surface, who had an entire life that happened before this one, a life that had been buried and hidden for reasons Sherlock could only guess at. Mary had told him some, in those two hours – she had grown up in foster homes. Her parents were absent, her mother too poor to look after her and her father incarcerated. However, she had excelled in school and found she had an aptitude for languages. She went to university in the United States and was recruited by the CIA, where she also discovered she had extraordinary skill with guns. She had felt she was doing something worthwhile, serving a country that needed her, but sometime in her freelance years the work had turned sour for her. Her childhood had been buried by the CIA; she buried a second life when she became Mary Morstan.

That first night at the restaurant, Sherlock had taken in an enormous amount of knowledge from Mary's face and figure, yet despite his conviction that she was a liar, his desire to hate her for taking John away, he had been disarmed by her kindness, by her mostly calm and even occasionally amused acceptance of his resurrection. Most women, upon having their engagement dinner interrupted, would have wept or raged; while Mary had been shocked and angry on John's behalf, she had not said a word about the way Sherlock had invaded what was supposed to be an intensely personal moment.

Sherlock wanted to be angry with her – had been angry with her, for a few overwhelming moments, when he realized that she had lied to John about who and what she was, when he thought she had manipulated the both of them for her own gain. Once he had eliminated that possibility, however, he was surprised to find that it was mostly compassion he felt.

Oh, he was still angry at her for deceiving John. Hypocritical it might be, but Sherlock had better reason than most to know what lies, both deliberate and of omission, did to John Watson. However, he also understood that Mary had wanted to tell John her story on her own terms – and Magnussen had taken that from her, backed her into a corner with very few available escape routes.

Five years ago he would have scoffed at the stupidity of it, trying to erase and forget a life that had obviously been lived under a series of identities and under government auspices, but five years ago there had been no John. Five years ago he had known neither the extent of Moriarty's network nor its utter depravity.

Five years ago he would not have understood the need to kill individuals who were simply beyond redemption. He did now.

Not Good?

No. Possibly not.

Yet – John had killed for him after two days, killed a man who had done much less than most of Moriarty's employees. And Mary, according to her own story, had simply targeted those she was asked to target by the U. S. government or by whoever was handing her a paycheck at the time.

Oh. There was a thought.

"All right, Mary Morstan," he murmured. "Let's see who you were."

He turned back toward the living room, located his laptop on the sofa, and swiftly strode over to it, hunching over the keyboard as he typed in his password, then plugging in Mary's thumb drive.

The drive opened to reveal dozens of folders, neatly ordered and labeled. "Childhood." "Education." "Recruitment." And then, a list of numbers.

The numbers didn't make any sense at first, until Sherlock realized that they were dates. Dates of her assignments, with no spaces or punctuation between the numerals.

Sherlock deliberately clicked on "Childhood" at the top of the list.

"'Begin at the beginning, and go on until you've come to the end,'" he murmured.

Over the next few hours, he read every scrap of information in every folder.

When he had finished reading all there was to know about Mary Morstan (née Angelina Gabrielle Renée Augustine), Sherlock finally looked up. It was late; judging by the darkness outside the window and the lack of traffic on Baker Street, it had to be nearing midnight. Not that the time really mattered. Sherlock hit a single button on his mobile and waited impatiently as the phone rang at the other end.

"Sherlock. To what do I owe the pleasure?"

"Spare me your sarcasm, Mycroft," he said shortly. "We have a problem."

"We?" Mycroft said incredulously. The use of the plural pronoun might even have ruffled his composure enough for him to raise an eyebrow, Sherlock thought scornfully.

"Yes, we," Sherlock answered. "Get me everything your minions have on Mary Morstan. I have to know what you know."

"Mary Morstan, as in John Watson's intended?" Mycroft replied slowly. "Whatever makes you think I have information on her?"

"Oh, don't patronize me, Mycroft," Sherlock retorted impatiently. "Of course you do. You monitor everyone who has any association with me, and even if you didn't, your job while I was away was to keep John safe. Naturally you would have vetted Mary when he started seeing her."

"Naturally," Mycroft returned dryly. "And why, if it's not too much to ask, do you need this information?"

"Because I need to know whether Magnussen knows anything that you don't, and how much of Mary's past the British government is aware of," Sherlock said bluntly.

The pause this time was loaded, not angry, but slightly dangerous in a way that only Mycroft was capable of.

"Magnussen?" he said carefully. "Charles Magnussen?"

Sherlock rolled his eyes. "No, our second cousin Victoria Magnussen," he said in exasperation. "Of course, Charles Magnussen. Really, Mycroft, are you getting that slow?"

"You are not to have anything to do with him, Sherlock," Mycroft said firmly. "I forbid it. You let him be, you do not get involved in any sort of case that will lead to him –"

"That would be rather difficult considering the case has already made its way to me," Sherlock snapped. "I already know much more than you about Mary, Mycroft, but I need to know what you know. Magnussen has information on her, he's blackmailing her with it, and we don't know where he got it. You know how he works; he's blackmailing her to get to me, and I won't let that happen."

Sherlock paused, catching his breath and reining in his anger, and Mycroft chose that moment to neatly upend his thoughts about the case.

"You're wrong about one thing, brother dear," Mycroft said tiredly. "He's not blackmailing Mary to get to you; he's blackmailing Mary to get to me."

Sherlock's mind went blank for approximately two seconds before all of the data in his head started to rearrange itself so quickly it was almost a blur.

"Say that again," Sherlock requested, his voice measured. Control. He had to maintain control.

"Charles Magnussen wants me, Sherlock, not you," Mycroft answered bluntly, his voice dripping with condescension, the earlier fatigue in his tone wiped away as if it had never existed. "I must give him points for originality; I confess I didn't think he'd go about getting my attention quite like this. I thought his blackmailing of Lady Smallwood was his latest gambit in my direction. This is decidedly more unpleasant."

"He went after Mary . . . to get to you?" Sherlock said in disbelief, starting to see the newly assembled picture in his head. "He believes I am your pressure point?"

"He never causes too much damage, Sherlock; he's a businessman. He wants my attention, not my wrath. He wants to make a deal of some kind, probably to do with increasing the ever-expanding influence of his media empire. It's inconvenient, but not insurmountable."

"Doesn't cause too much damage?" Sherlock repeated, his voice rising. "Have you missed the events of the past few months, brother dear? He kidnapped John. He put John in a bonfire, indirectly putting both Mary and myself in danger. Now he's blackmailing Mary, forcing her to reveal her past before she was ready, possibly as a prelude to forcing her to do his bidding. Magnussen attacks people who are different and preys on their secrets; why haven't you gotten rid of him?"

"He's occasionally useful to us; a necessary evil," Mycroft said calmly.

"A necessary evil?" Sherlock hissed indignantly. "He's gone after your co-workers, caused you any number of political headaches, and now he's coming after your brother, whom you claim to worry about so very much, in order to get to you – and he is necessary?"

"He's a media and political manipulator, Sherlock, not a dragon for you to slay."

"He's a blackmailer, Mycroft, a leech. A predator. A blight on your precious kingdom," Sherlock said coldly. "You are going to give me the information I require, you are going to help me, because I refuse to let John's happiness be destroyed; do you understand? Otherwise, I will find a way to do it myself, even if I have to hand you to Charles Magnussen in handcuffs."

"Heaven forbid," Mycroft said with a sigh. "Thank goodness you chose to inform me of this now, Sherlock; otherwise who knows what wild scheme you would have come up with to save John and Mary. I will help you, if only because I would rather know what you are up to beforehand, rather than after the fact."

"Thank you. Your compassion and concern are astounding," Sherlock bit out. "I'll expect the files on my e-mail as soon as –"

"Also, your loss would break my heart," Mycroft interrupted quietly.

Sherlock's power of speech abruptly abandoned him. Mycroft, of all people, never said such things. They never said such things, only inferred them and alluded to them in veiled hints and verbal sparring. It was contrary to all of their interactive protocol as siblings, built up over years of rivalry and competition.

"What the hell am I supposed to say to that?" he sputtered finally, after who knew how many seconds.

"Nothing at all, brother dear," Mycroft answered, his usual disdain and superiority back in place but marred by something . . . poignant. "Nothing at all. I'll have the files to you within two hours."

You left out one crucial piece of information. – SH

Yes. Understandably, wouldn't you say?

How much did he pay you? – SH

Enough to get out, which was all I wanted.

And you would have done it? – SH

At the time, yes. I didn't know you, Sherlock. Either of you. And meeting John afterward really was entirely coincidence. Wonderful coincidence, as it turned out.

That doesn't mean he'll forgive you. – SH

I know. Do you? Forgive me, that is.

Sherlock took a long time to ponder that before he answered. When he had found this particular file on Mary's hard drive the night before, he had become perfectly still as cold terror had washed over him. All he had been able to think about was how close Mary had been to John all this time. Had she been other than she was, everything he had done to keep John safe would have been in vain

However, she was not anything other than herself: warm and caring, fierce and determined, and absolutely devoted to John – and against all probability, to Sherlock. She had given John an emotional home when he had none, done her best to smooth things out between Sherlock and John when the detective came back, and showered Sherlock in snarky affection. That last job had meant the end of her old life, a life she had wanted to be rid of, and Sherlock supposed that in her place, he would have done the same.

I think so. Regardless, I will not let you become another of Magnussen's victims. Everything about him is vile. – SH

Well, that gives me something to go on, anyway. Thank you. And you'll get no argument from me about Magnussen.

By the way, has anyone ever told you that it's odd to initial your texts?

Sherlock couldn't help the smile that curled up his mouth at that last.

John has mentioned it once or twice. – SH