The death of Mary was a shock to everyone, especially Molly Hooper. Molly hadn't had many female friends, and she became very close to Mary in her final months. Losing her felt like losing a sister, although Molly could see nobody hurt more than John and poor little Rosie.

Taking care of Rosie in the early months after Mary's death was one of the only things that keep Molly going, but over time she couldn't help but feel guilty over all the things that she got to see and what Mary didn't.

Over time, Molly knew that she had to do the one thing she swore she would never do: use her superpower. She was going to trade places with Mary.

At first, Molly tried to tell herself it wasn't a good idea, but as time went on, she realised it was the best option. John and Rosie were hurting, and she could fix it.

She didn't have any family left - a few friends at Bart's, and maybe Toby, but nobody overly important. In time they would forget her, and she would just be another name of someone they knew from long ago. Even Sherlock wouldn't see her death as anything more than a sad event that happened. Knowing him, he would probably delete her from his mind (although a selfish part of her wanted him to be as devastated as she would be over his death.)

Molly knew she would miss doing her job, not being able to help Sherlock on cases, or being there for Rosie. She hoped people would tell Rosie who her godmother was and how much she loved her. But Rosie didn't need a godmother if she could have her real one back.

As she got her things together, she left letters for loved ones she would leave behind. One for the people at work. Mary and John. Mrs Hudson. Greg. Mycroft. Even Sherlock. She knew it was possible for some people to remember the true events, so these letters would be a way to explain herself. Molly hoped that the one person who wouldn't remember would be Mary, because there would be a chance that everything would go back to the way it had been before and everything she had done would be for nothing.

When everything was sorted, and she said goodbye to her friends (even though they did not know it was goodbye), Molly walked back to her flat alone. When opening the door, she was greeted by Toby. Molly bent down to give him a quick pet, before walking into the kitchen to make sure he was fed. It seemed stupid, but she knew that she was going to really miss that cat. She hoped he would have a good home after she was gone.

"I'm going to miss you," she whispered into his fur.

When Molly was ready, she closed her eyes and imagined being in Mary's place from all those months ago. It happened so quickly: one moment she was in her flat, the next she was stood next to Sherlock in the aquarium.

Then she jumped, and took the bullet for him.

It hurt like hell, all her insides burning. 'How did Sherlock survive this?' She asked herself. Molly felt herself getting weaker by the second. In front of her, she could see Sherlock next to her on the floor; he was yelling at John to do something to help, though everyone knew it was too late. Molly's fate had been sealed.

"No, Molly, stay with me, okay?" He said to her. "Everything is going to be okay. Please."

Molly never thought she would see the day where Sherlock would beg for something, but now, here he was, asking her to do the impossible.

"I'm sorry, Sherlock." With her last ounce of strength, she held herself up enough to whisper four last words in his ear. "I love you, Sherlock."

And just like that, she slipped away.

Sherlock woke up from his dream. It was the same one he had been having ever since Molly died. It was her death, repeatedly playing. He was driving himself close to insanity. He'd always heard her last words - how sweet but how painful there were at the same time. He wished she had more time for him to reply. He wanted to be with her, but he knew he needed to stay alive. It was what Molly would have wanted.

Sherlock had thought about touching drugs again, but knew Molly would be more than mad at him. He promised her, long before she died, that he would never touch drugs again, not even if it was important to a case. He wasn't about to break a promise like that. Especially when that person meant so much to him. He also needed to stay alive for Toby, Molly's cat. Before Molly's death, they got on because they had to, but since her death, they became closer. He was the only piece of Molly that was left, and he couldn't bear to see him go. He always wanted a dog but instead, he got a cat.

Mary had been a big help to him since it all happened, although Sherlock couldn't shake a feeling he always got when he was around her. He'd never tell anyone, but she somehow seemed colder, like she didn't fit anymore. Sherlock kept telling himself that it was maybe just her way of grieving, but it was an odd feeling he got around her.

Mary came to Baker Street most mornings to bring his goddaughter over in the hopes that it might cheer him up. Rosie always seemed to bring a smile to his face, though it was tinged with sadness. Mary never asked, but she knew why.

"You really love your uncle Sherlock, don't you, Rosie?" Mary said, handing over her daughter to the detective.

Rosie started to giggle, seeing her godfather. Mary couldn't help but smile, knowing that when she was older Sherlock would never be able to say no to her. She couldn't wait for that.

"I think she looks more like you than John. That's probably a good thing for her sake," Sherlock said, looking at his goddaughter.

"Lucky her, then." Mary laughed. She was glad to see that Sherlock had gotten dressed today. She knew that Molly's death had taken its toll on him. Mary wasn't stupid; she knew Molly had meant more to him than he ever let on and now he was grieving for what could have been. "So, how are you today, Sherlock? Feeling any better?"

Sherlock kept his focus on Rosie. "Just because you ask that question every day doesn't mean I have to answer it every time."

"So not too great today."

Sherlock chose not to answer.

"Mrs Hudson told me she thought she heard you playing the violin last night. Is that true?" Mary asked.

"I guess that's true," he replied.

"Is that the first time you've played the violin since -?" Mary couldn't bring herself to end the sentence.

"Since Molly's death? Then, yes," Sherlock said quietly, more to himself than Mary.

"That's good, Sherlock. You're starting to feel better," Mary told him.

"I don't want to feel better. I want Molly back. I can't do any cases. It doesn't feel right; she was the best pathologist Bart's had. She set the bar too high."

"I know, Sherlock. I miss her too. We all do."

"But you don't understand...I never got to tell her..."

"Tell her what, Sherlock?" Mary asked him, even though she was pretty sure she knew the answer.

"I never told her I loved her," Sherlock said, starting to cry.

"Oh, sweetie she knew," Mary said, giving him a hug.

"She did?" He asked like a small child.

"Of course, she did," Mary said, holding him close to her.

Not long after Mary left, Sherlock received a few texts from his brother, offering some case. Sherlock didn't want to do any cases; he was not in the mood. There was only one other place he would rather be right now: Molly's flat.

In her will, she had left her flat to Sherlock. Molly knew that it was his favourite bolthole, and there wasn't anyone else she could imagine leaving the place to. It was his place as much as it was hers. Sherlock never told anyone, but he was very grateful.

There were times like today when he would just let himself into her flat, sit on her sofa, and pretend to be in his mind place and, just for a moment, let himself think she would be back from work any minute. Molly's flat was just as she left it; Sherlock couldn't bear to throw it all out. It was Molly's stuff, her life - nobody else could have it.

Sherlock found himself walking into the kitchen. It was the one room he hadn't been in since Molly's death. This was the room that they spent the most time in, whether they would talk about cases, eat food, or just talk. He half expected her to be in the kitchen cooking something. She always made sure Sherlock ate something.

He found her phone on one of the countertops. Many a time, he wished he could call her - she would always pick up for him - just to hear her voice one more time. That was all he asked. He couldn't help himself, but he picked it up. Stood in the kitchen where Toby's food bowl had been, he could feel himself wanting to cry.

It happened suddenly, but a flash of images happened in Sherlock's mind: instead of Molly, it was Mary dying on the floor of the aquarium in John's arms. Then it was Molly, looking at Rosie.

He remembered now.

Sherlock couldn't understand it how had Molly done it. How did she change places?

Then, more images flashed before his eyes: there was Molly, stood in the same place he was, holding her phone, telling him she loved him; him waking her up in the middle of the night to tell her he was sorry and that he meant it; a brief vision of just the two of them getting married. Then, a slight glimpse of children: perfect mixes of him and Molly, with either brown curly hair or straight black hair, and blue eyes that were so beautiful and happy.

Was this what their life was meant to be like? Sherlock felt faint. He didn't know what to do.

"Oh, Molly, what did you do?" He whispered to himself. Then, in front of him, he thought he saw a figure, leading him towards Molly's bedroom. As he followed it, he saw it standing by her bedside cabinet, pointing at the top drawer. He walked over to it and opened it; he was surprised to see an envelope with his name on it inside. Sherlock sat down on Molly's bed and began to read.

Dear Sherlock,

If you are reading this letter, you have remembered and know the truth. I'm sorry that you have remembered the true events, but I am not going to apologise for what I have done. You might not see it now, but it was the best choice.

I did it, so Mary, John and Rosie could be a family. She needs her mother more than a godmother. Please don't let her forget me, and let her know that I loved her very much.

I'm going to miss you a lot more, Sherlock. I hope more than anything you can find happiness and, if you want to, find someone who loves as much as I do or even more.

I have loved you since the moment I saw you and I always will. Just promise me one thing, Sherlock. Don't delete me like one of your experiments. I think we're friends, so just don't forget me, okay?

Until the next time,

Molly xxx

"Oh, Molly. My Molly," he said to himself.

Sherlock read and reread the letter before he almost knew it by heart. He needed to think. He needed to do something. He needed his Molly back. What would Molly tell you to do right now? He thought to himself. "Everything is always clear after you have a little sleep." He remembered her telling him once so that's what he did.

For the first time in months, he didn't see Molly's death. He had a perfect dreamless sleep; to Sherlock, it was absolute bliss. When he woke up, he knew exactly what he needed to do. He needed to make others remember, and Sherlock knew the first person he needed to talk to.

He all but ran straight to John and Mary's flat; he didn't care what the time was. He needed to talk to Mary. Alone.

When John opened the door, he looked less than happy to see the detective. "If you are here to ask me to go out on a case with you, it's not happing, Sherlock."

Sherlock acted as if he didn't hear anything his friend had said. "I need you to go out. Take Rosie to the park. Don't come back for a while."

"Sherlock, it's nine o'clock at night. Rosie's in bed," John told him, feeling a bit annoyed.

"Oh, then go to the pub," Sherlock said, throwing his wallet at John. "That should be enough in there to keep you going for a few hours."

John looked at Mary, stood behind him, who was giving him a look that said, 'you should probably do as he says'.

When John had left, Sherlock turned to Mary. "It should have been you who died."

"Excuse me?" Mary said, not quite believing what Sherlock said. "Did you say that I was the one who should have died?"

"Yes, that's exactly what I said," Sherlock said, as if it was the stupidest thing in the world. "I remember clearly now. Oh, Molly, she's so clever. She thought she was doing the right thing."

"Sherlock, what are you talking about?" Mary asked him.

"Molly swapped places with you," Sherlock told her. "In the original timeline you died taking that bullet for me, not Molly. You have to remember. Please, remember."

"Sherlock, are you okay? You haven't taken anything, have you?" Mary asked, concerned.

"No, I haven't. I wouldn't. I need to make you remember like I did."

Mary decided to play along with Sherlock; it was the happiest she had seen him in months. It was like he had hope again. She wasn't about to let that go quickly. "How did you remember, Sherlock?"

"I was stood in Molly's kitchen. I picked up her phone and suddenly I had images flash in my head, and I remembered. I had other visions, of stuff that I have never seen before. I think it would have happened in the future, if Molly didn't die."

Mary couldn't help but feel curious. "What did these 'visions' look like, Sherlock?"

"It was of me and Molly, us telling each other about how we felt. I think there was a wedding, and kids that were beautiful, and we were so happy."

Mary felt her heart ache for him. He was talking so happily about these things that weren't going to come true. "Did anything else happen?" Mary asked.

Sherlock had almost forgotten, but pulled out a letter from his pocket. "After the visions, I saw this ghost-like figure. I think, looking back now, it looked like Molly. She led me to this letter. It wasn't there before. If you read, it will make sense, I swear," Sherlock said, handing the letter to Mary, who looked at it. "Don't you see it? It all makes sense now."

"Sherlock, I don't see anything. The page is completely blank," Mary told him.

"No, it can't be. It has words - why can't you see them?" Then the answer hit him. "Oh. It's because you don't remember. Maybe if you did then you would see the words. Look, let's got to Molly's flat."

"Sherlock, we can't. There's nobody here to look after Rosie after you sent John away. Look, how about we go in the morning? I can see if Mrs Hudson would look after Rosie. You can stay in the guest bedroom, if you like."

Sherlock knew this might be his only chance, so he wasn't about to piss Mary off. "Okay."

When in the guest bedroom, he knew he would not be able to sleep. Instead, he thought up all the things he would say to Molly. Even if this was going to be his only chance, he needed to work out all the important things. He didn't want to regret this.

As soon as Rosie was dropped off, Sherlock and Mary got a cab to Molly's flat. Mary had no idea what was going to happen, but she hoped Sherlock was going to be okay. She hoped this wasn't going to be the thing that pushed him over the edge.

When they were in the flat, Sherlock directed Mary to the spot he stood. "Stand just here."

"Sherlock, I don't see anything."

"Think about Molly."

So Mary did, and almost instantly she had visions flash in her mind. She saw Molly's death, but then it changed, and he saw it as her own. She remembered now. Mary felt numb with grief all over again, and could not believe the sacrifice that Molly had made.

"Sherlock, I remember," Mary whispered. When he didn't respond, she turned around and saw that Sherlock's attention was on something else. Something better.

There, right in front of Sherlock, was Molly. She looked like her normal self, but at the same time, she didn't. Sherlock looked at with such a mix of wonder and sadness.

"Molly," he whispered to her "Is that you?"

"Yes, Sherlock, it's me."

"Molly, I've missed you so much." Sherlock stepped forward to touch her, but was sad when his hand went right through her.

"Sherlock, I've missed you too. So much. But I don't belong here anymore." She turned to see Mary was also in the room. "I did what I did so you, John and Rosie could be a family."

"Molly, you didn't have to do that," Mary said.

"I did. I didn't have any family, nobody to leave behind. You did. It was the right thing to do."

"You had me," Sherlock yelled. "Can have me. You're my family."

"Sherlock, please, don't," Molly said, trying to calm him down.

"What about our family?" Sherlock asked her.

"But we don't - we're not -"

"I had a vision, Molly. I saw them: our children, or what could have been them. They were so beautiful. Molly, I love you."

"I love you too, Sherlock."

"Is there a way I can get you back? Can we swap someone in your place? We could substitute Anderson."

Molly couldn't help but giggle. "I'm sorry, Sherlock, but that's not how it works."

"But there has to be a way, right?" He said hopefully.

Molly hesitated.

"I have to swap back with you, don't I?" Mary asked.

Molly didn't answer, but the look on her face told her everything.

"I'll do it." Mary said, without hesitation.

"No, you can't," Molly said. "You should see your family. You need to be with them."

"Molly, you deserve that. This idiot too." Mary said, pointing at Sherlock. "I got these extra few months with them and I am ever so grateful for that, thank you."

Mary knew what she needed to do. It was in her mind, clear as day. She stepped forward and grabbed where Molly's hand should have been. "I choose to take my place back, change things back to the way they should be."

In a flash of light, Mary was gone, and Molly was back in her human form. She fell forwards, right into Sherlock's arms.

"No, "Molly said. "This should not have happened."

"But I have you back," Sherlock said, holding her close to him. "It's odd. I have memories of both timelines. Mary's death and yours."

"Really? That's all you can say right now," Molly said, feeling upset with the detective.

At that moment, Molly's phone began to ring. Sherlock grabbed it off the countertop for Molly. When they saw who was calling, they both seemed a little shocked.

"It can't be...can it?" Molly said, looking up at Sherlock.

"There's only one way to find out."

"Hello?" Molly said, taking the call.

"Molly! You're back. It worked," Mary said.

"So are you? But how?"

"I don't know. Do you?" Mary asked.

"Well, I mean, I think I do. But I thought it was just an odd tale my dad told me. He used to say if a person is brought back by the person they replaced, and that they'd been alive for a set amount of time, both will live and only the people who know the true events would remember. Everyone else will act as if nothing has happened."

"So, John won't remember that either of us died?" Mary asked again.

"He won't have a clue. Life, to him, will be as if nothing happened," Molly told her.

"Wow. Just, wow. This is amazing. Look, Molly, I would love to stay and chat, but I need to get Rosie from Mrs Hudson."

"Okay, please, give her a hug from me."

When Molly hung up, she looked at Sherlock. "That was Mary. She's alive. She couldn't talk much because she had to go pick Rosie up from Mrs Hudson."

"You're both back," Sherlock said, smiling.

"Life's going to go back to the way it was before now, isn't it?" Molly said quietly

"Yes," Sherlock said. "Well, and no. Life for Mary and John will be the same, but, for me and you, Molly Hooper, life is going to change so much."

"It is?"

"Oh, absolutely," he said, leaning down to kiss her.

Sherlock and Molly had the rest of their lives to live and they could not wait to do that together. They had both found what they didn't know what they were looking for: their family.