A/N: This crept into my head tonight, and I had to get it out. Because I compressed a potential story into a one-shot, there may be questions - please let me know in a review and I'll try to clear them up in the story so it satisfies.

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Months. It had taken him months to get all the right information lined up, all the strings pulled in the right order, every favor he'd ever doled out called up. And now he was so close. There was just one more loose end. And he was standing in front of her door.

He rang the doorbell, and a harried woman in jeans and a flannel shirt, her hair a mess and her eyes hinting at too little sleep opened the door promptly. "Can I help you?"

"Yes, I believe you can, Mary." Sherlock's voice held nothing, no indication of why he was there. Her eyes squinted, though, and he knew she understood.

"Come in then. I'll put a pot on and we can chat."

"No, no tea, thank you. But let's do have that chat."

Her eyes were wide, but she seemed more resigned than surprised. "As you like. Come in all the same." She held the door for him as he went past her and up the hall. She closed the door to the bedroom out of habit as she walked past, knowing he'd already seen and tallied the mess she'd made of the space in her frenzied packing. She sat down with a rush of air before Sherlock had even fully turned to face her. "So, you're alive. I'm…" she drifted off.

"You're what?"

"Incredibly glad for that. I didn't believe him, not really, for all these months. That you were alive. I didn't believe it when Jim said that you might be alive. He told me you would be, but in the end, I just couldn't believe it."

Sherlock flexed his fingers against the leather of the armchair. It was a good, steady chair and it reminded him of the flat he had shared with John. He blinked and reorganized his thoughts. Now was not the time or the place to be thinking of John. He had to straighten out this, the last connection to Moriarty, before he could finally see the only friend he had ever had. Then John would be able to know the truth without being in danger.

When Sherlock didn't respond, Mary went on. "He left a note. Before he went to meet you. I think he knew he wasn't coming back, one way or the other. And he felt some need to tell me, I suppose, to tell someone… someone who might grieve for him." She bit her lip, chapped lips that looked like she often worried them like this. "It laid everything out. And…" She took a deep breath. "And he sent me something, in case you ever came calling."

She went to stand up, then hesitated. "It's a gun. It's in the left hand drawer of the coffee table, along with the note."

Sherlock watched her, evaluating whether it was safe to reach into that drawer. The drawer was within easy reach for him, but she'd chosen her seat first, so perhaps she had wanted him to go into the drawer. Maybe, like Irene Adler's safe, it contained a self-firing mechanism. From what he knew of her though, this innocuous-looking school teacher wasn't the type to kill a man without giving him a chance. She was dangerous, if she wanted to be, but there was something she wasn't yet saying, he sensed, something she desperately wanted him to figure out. She wouldn't kill him yet. He opened the drawer.

The gun was exactly the same as the one that Moriarty had shot himself with there, at the end. On the roof of St. Bart's when everything had been solved and gone to hell at the same time. What was it that he'd said? That he was on the side of the angels? But oh, he most definitely wasn't. Moriarty hadn't succeeded in burning the heart out of him either. It was Sherlock, not Moriarty, sitting alone in a flat with the one woman that Moriarty had ever seemed to trust. And she was showing him the gun she was supposed to kill him with. He would make her answer the questions he had, the few that were left even now. What was she, that she would befriend a monster?

"He said if you ever came around, to make sure I used this on you. That you'd be out to hurt me, to get revenge for everything." Her voice grew quiet and strange. "I always knew he was mad. I even tried to ignore all the truly evil things he did. And I thought he really did care about me in his own weird way." She looked up from the gun to Sherlock's face. "He did, I think. Though he just didn't know how to care, didn't know how to show it. He was broken that way." She took another deep breath. "But you did come around; he knew that much about you. Why?"

"Why?" Sherlock frowned at the obvious question. "Because you are the only person in the world that Moriarty communicated with regularly. He had dinner at your flat the night before the incident. Because he didn't even have the semblance of caring for anyone else. And a woman matching your description, but veiled in black, was at his graveside, a funeral no one else dared attend."

"No one should go into the earth unmourned." Her voice was strong now, but the grief of that moment over a year before was still full in the sound of it. Sherlock wondered if John had ever sounded like that – loud and hollow, as though everything he said was echoing through a large metal bowl.

"But there was no reason for him to need you. You weren't in any criminal circles. You had no significant connections. You aren't particularly clever. You had never even contacted me. So why did he want to talk to you when he was playing his end game?"

"Because he was afraid, I think. I've wondered the same so many times since meeting him. More since he died. Even though he could think of all these possibilities, it was still a suicide. There was still a note. There was still that little bit of fear about going into that good night and all." She paused, pressed her lips together, met his eyes. "But I wonder why I trusted him. Why I took the parts of him he showed me first as gospel truth and everything else as unfortunate side notes." She bit her lip. "I don't know, Sherlock. I don't have the answers."

"You do! You do have the answers! You know about his last plans, because he was afraid - afraid that no one would be left alive to recognize his sheer genius. And so he told you." Sherlock's voice was low and deadly, assured of itself and desperate all at once. He needed things from her, and he'd be damned if she couldn't give them. "Do not lie to me, Mary Morstan."

Her breath caught, and she settled back into the sofa more firmly. "Now there's a name…" She closed her eyes for a long moment. "I suppose when you're dead, some of your research gets a bit dated. But I haven't gone by that name in a while."

"Change your name, too? Didn't want anyone else making the link between the good old-fashioned school teacher and the consort of a criminal mastermind?" Sherlock didn't know why he was so angry all of a sudden. Something was trying to assert itself on his consciousness, but it wasn't very clear just yet.

To his surprise, she remained calm. "A woman often changes her name when she gets married." She didn't say anything else. Sherlock's fingers molded into the dents on the leather chair and his stomach dropped, horrified. He tried not to shake, tried not to show her what her simple statement was doing to him.

"Was this…" he wet his suddenly-dry lips with his tongue. "Was this part of the plan all along? To burn the heart out of me?"

Mary's eyes filled with tears that she blinked back. "No. Never. I didn't even know John existed until he came to my door one day, presumably following the same trail you did. Maybe a month after the fall? He wanted answers. Answers I didn't have then and that I don't have now." Her hand lifted as though to put it on top of Sherlock's in a gesture of comfort. It hung awkwardly in the air for a moment as she reconsidered, then put it back in her lap. "We've only been married a month or so. Most of his things aren't here yet." Her eyes lingered on the chair, and they were so full of sorrow and sympathy and something else unspoken that Sherlock couldn't look at her.

He stood violently. "You're lying. John wouldn't marry. He could barely hold onto a relationship long enough to get them in bed."

"He held on to you," she said quietly. She played with the edge of a blanket that was draped over the sofa.

Sherlock felt his stomach crumple with the words. He'd been beaten, stabbed, shot, filled with shrapnel, and collided with the sidewalk at a reasonable, if not lethal, speed. But it had never heart like this. Moriarty's voice filled his head: "I will burn you. I will burn... the heart out of you."

The sound of a key in the lock startled both of them. "Stay here," she whispered. "I'll just… he won't do well if he just sees you. He's missed you so much. It nearly killed him." She gave Sherlock a pleading look. "I'll just tell him, and then I'll go." She paused by Sherlock's side, touching his arm lightly. "I am sorry, Sherlock. But I do love him. More than I ever thought I could love anyone. And every day I hate myself for the part I inadvertently played in hurting him. In hurting you. And every day until today, he has forgiven me for it. But if…" her voice broke, but she cleared her throat and continued. "If today he doesn't forgive me, if he sees you and everything changes and you take back that place in his heart…" she met his gaze, unable to finish her sentence, but Sherlock understood.

He would not understand how a demon like Moriarty would have survived an association with an angel like this woman. He would spend hours and days and lifetimes considering that. But at that moment, it was all he could do to grapple with the idea that John was just outside the door. That John was married to the woman he'd thought the only threat left. He nodded, swallowing against tears, and sat back down in the chair as she walked out. He listened to their conversation in hushed tones, including the startled little squeak that could only come from John. Her offer to leave, and his pleas for her to stay with him. Then the slow double footstep of man and wife, hand in hand, as they walked down the hall from the door to the living room where he sat.

His heart was on fire.