Sherlock sat his son on a chair in the kitchen and tucked him into the table. "Then when I say: 'show her' you will hand her the dish, okay?"

Vaughan pulled the microscope towards himself with an excited grin. "Yep."

"Are you absolutely certain?" he crouched down, bringing him level with his eyes. "you hand her the dish when I say what?"

Vaughan rolled his eyes. "When you say: 'show her'. It's easy."

Sherlock nodded and stood up, exhaling slowly. He stuffed the ring box up his sleeve, practicing letting it drop into his hand and opening it in one fluid movement. He took a marker pen from the drawer and held up a Petri dish, carefully writing 'will you marry my dad?' On the bottom. 

"What does that say?" Asked Vaughan as he picked it up and began to sound out the letters. 

"Nothing it's a surprise," he replied, taking it away from him and putting on the table. 

A bustling sound came from the living room. The unmistakeable sound of Margaux getting home from work. Every day she would do the same things in the same order: coat off, bag on the couch, sit down, shoes off. 

He put the goggles on Vaughan's face – which almost immediately slipped down his small button nose – and sat him in front of the microscope. They waited for just a moment before Margaux appeared in the archway of the kitchen. 

"Hello," she began. "What are you two doing?" 

"Blood samples," said Vaughan, exactly how they had rehearsed. 

She glanced across to Sherlock and frowned. "Love, I told you no more of this." 

"No more what?"

"This..." she gestured to the table. "Blood samples, dangerous chemicals, taking him along on cases. It's rubbing off on him."

"Well I know that but..."

"He has a bedroom full of toys, shelves of books, yet you're in here showing him human blood." She sighed. "His teacher said–"

"I know what his teacher said," he interrupted, trying desperately to keep his plan on track. "I just wanted to show you–"

"Look, I realise I haven't been perfect either but I'm trying my best here; I'm watching what I say, I've stopped bringing work home, I need to know you're trying too."

"I am, Margaux, I am, just... come and sit down a minute."

She remained standing and folded her arms. "Sherlock, I love the relationship you two have. But you should be able to transfer it other things – age appropriate things."

Sherlock sighed. He slid the ring box down his sleeve and pushed it back into his pocket; it clearly wasn't the time, and this clearly wasn't the way to do it.

Vaughan let out a grumble and looked up at his mother. "Mummy, I'm going to be a detective–"

"Yes, darling, I know you are. But right now, you're not a detective, you're four."

He threw his goggles onto the table, jumped down from his chair and stormed past her. Margaux turned around, listening as he stomped up the stairs to his room. Sherlock picked up the petri dish and wiped away the message, putting it in the sink before she turned back around.

She looked at him sympathetically. "I haven't even been home five minutes and I'm already his biggest enemy."

"He's stubborn," said Sherlock as he sat down. "I think... Maybe... he might get that from me?"

"Maybe." She laughed before sitting next to him. "I'm sorry I ruined your fun. It's just... not even a week ago, I sat in that classroom and got made to feel like the worst mother in the world."

"I know." He reached over and squeezed her thigh gently.

Margaux smiled. She felt guilty; she had entered the flat like a tornado, disrupting the calm and spoiling their evening.

She looked at the apparatus laid out on the table. "What was it you wanted to show me?"

"Hm? Eh, nothing."

He slid his hand into his pocket, grasping the box in his fist. Attempt one had failed. He wondered how many more there would be.

*

Margaux woke to her phone ringing in her pocket. She sat up, realising she had fallen asleep next to Vaughan while putting him to bed. He remained asleep, rolling over and kicking his legs out from under the covers as she took out her phone and answered it quietly.

"Hello?"

"Did I wake you?"

She rubbed her eyes and brushed her hair out of her face. "No... No, what's up? Where are you?"

"Mycroft's. Well, I was, but I just left."

"What were you doing there? It's almost midnight."

"I had to meet with him to discuss something," Sherlock replied. "It's raining, can you come and get me?"

She climbed out of bed and glanced out of the window, at the rain pelting the ground like marbles.

He continued. "I'd get a cab but–"

"No, don't be silly. Of course I'll come and get you. Just give me twenty minutes."

She went into their bedroom, flicked on the lamp and slid open a drawer. Over her turtleneck top, she pulled on a jumper, and over that she threw on a large checked shirt. She picked up her waterproof jacket and a pair of lace-up boots and made her way downstairs.

Mrs Hudson answered the door cautiously, relaxing when she saw Margaux on the other side. Her brow came together when she watched her crouch down to tie her laces.

"You're going out now?"

"Sherlock called, he needs me to pick him up from Mycroft's. Vaughan's in bed so would you mind sitting upstairs while I'm gone? We shouldn't be long."

Mrs Hudson gave a kind smile. "Honestly, I don't know what you two would do without me. I'm like a live-in babysitter, might start charging for my services."

Margaux laughed. "And I would happily pay because you're brilliant."

"Go on, dear. I'll go up in a second."

"Thank you."

She stepped outside and shut the door behind her, pulling up her hood before running down the street towards her car. When she got inside, she took a moment to catch her breath, watching as the rain thrashed against the windshield creating a deafening white noise. She turned her key in the ignition, cranked up the dial on the heating and switched on her music, flicking through songs as she began to drive.

...

When she pulled up outside Mycroft's home, she saw Sherlock standing outside. He had pulled up the collar of his coat, but it hadn't done much to stop the rain from soaking his hair, flattening it to his head and dripping water down his face. He climbed in and leaned back against the headrest.

"He could've let you wait inside," she laughed as she looked him up and down.

"We got into an argument and I stormed out. It would've ruined the drama if I asked to come back in."

"Honestly, you two."

She pulled away slowly. The windshield wipers swinging from side to side like a metronome.

"Thank you," he said.

"Oh, I don't mind. Probably wouldn't do it for anyone else, but since it's you..." she smiled.

They drove for a while in comfortable silence through the unusually deserted London roads. Sherlock rested his head on the window, watching the streams of rain catching the light as Margaux hummed softly to the music playing from the radio.

"I apologise," he said, his forehead pressed against the glass.

"What for?"

"For earlier with Vaughan. It was a stupid idea."

"It wasn't stupid. It's just... He's like a sponge, I suppose we have to be more careful about what he's absorbing." She laughed to herself. "Sometimes I think we should just drop the 'Cave' from his name; he's almost completely yours."

Sherlock turned to look at her. "He's too nice to just be mine."

She rubbed his arm appreciatively before returning her hand to the gear stick.

"Also, don't let his teacher get to you; you're a good mother," he added.

He had never said that before. She was sure he'd thought it, but hearing it was a different feeling entirely. She almost felt like she could cry, shaking away the feeling with a smile.

He went quiet after that. She glanced at him a few times in the wing mirror, noticing the lines in his forehead as he thought hard about something. There were a few moments when she almost asked him what he was thinking about, each time changing her mind and leaving him to brood.

He lifted his head suddenly, peering out at the road in front of them. "Turn left there."

"Hm? Why?"

"Here, turn here."

She flicked on her indicator and turned left, following the road until he gave her another direction. Before she knew it, he had led them in the opposite direction from home.

"Are you taking me on a case?" she asked.

"Just go there."

She shook her head. "That takes you to the museum carpark."

"Yes, that's right."

"Why do you need to go there? It's after midnight."

"Will you trust me?"

"You're roping me into something dodgy. I just know it."

They pulled up in the empty carpark, climbing out of the car and rushing through the rain to the museum.

"Are you soliciting me into illegal activity?" asked Margaux.

Sherlock laughed. "No." He paused. "You're doing it for free so it's not solicitation."

"Sherlock."

"I'm joking, no, just come on."

She followed him around the building to a large set of glass double doors.

"Any normal woman would tell her boyfriend to pack it in and leave. But for some reason, I'm still here."

Sherlock shook the handles – locked. He cupped the sides of his eyes and pressed his face against the glass. A torch light shone from inside. It turned swiftly, pointing in their direction and approaching them.

Finally, a night-watchman unlocked the doors and opened them, his keys jingling in his hand. He was large and bubbly, with a round, bald head hidden under his security hat.

"Hello, Sherlock! How are ya?" he asked.

"A little... chilly." He gestured to the weather.

"Oh of course, of course, come in."

"Thanks Kev."

They stepped inside, shaking off the cold rain that had clung to their clothes.

"Oh and Sherlock," said Kev as he locked up behind them. "Don't touch nothing."

Sherlock winked at him before strolling away with Margaux by his side.

"Does everyone in London owe you a favour?" she asked.

"I find favours a much more effective currency."

...

They walked around the museum together. The lights were off, the exhibitions quiet and still. There was something eerie about being the only people in such a large, echoing building.

"So, I take it you're looking for something?" asked Margaux.

"Nope. Just felt like a walk around. Without the crowds."

She looked up at him and giggled. "You know when I was younger I'd have loved this. I used to come here all the time."

"What for?"

She shrugged. "It's free, it's warm, they have quiet nooks where you can sit and read."

"It's a place to hide from emotionally abusive mothers."

"That too."

They held hands as they walked through the displays, offering facts to one another and using their phones to shine light on the descriptions. Eventually, they found themselves in a large room with high ceilings and a marble floor.

"This was the room where they had the ball," said Margaux as she looked around in awe. "I wonder if you can still get out onto the balcony upstairs."

Sherlock's eyebrows raised for just a moment. It was almost like he could feel the lightbulb hovering above his head. "Why don't we go and see?"

She nodded and took his hand again, allowing him to lead the way.

...

He used his elbow in a smooth, forceful manoeuvre to pop the doors open. A siren sounded for a second, stopping suddenly like the bleeping of keys silencing a car alarm. 

"Good old Kev," said Sherlock as he stepped aside to let her walk out onto the balcony. 

"He told you not to touch anything," she chuckled. 

"He knows better than to assume I'll listen."

It was still raining. Margaux flipped up her hood and leaned against the railing as she looked out across the London skyline. Sherlock stood beside her, ignoring the cold that nipped at his cheeks. 

Margaux laughed to herself. "I told Mrs Hudson we wouldn't be long."

"I'm sure she'll understand when we tell her where we've been."

She paused. "Promise me you'll never stop doing things like this... surprising me, paying attention to memories, revisiting lovely moments."

"I promise." He pushed his hands into his coat pockets. "Though I wouldn't say this was a 'lovely moment', last time we stood here you almost got shot."

"Ah yes, the first time I got threatened with a gun. Little did I know there'd be plenty more times after that. It's funny, no one ever tried to shoot me until I met you. Then bam! Museum, Moriarty, Eurus..."

"You need to stop rubbing people up the wrong way." 

She snorted out a laugh.

He grinned, his eyes creasing at the corners. "It seems such a long time ago now."

"It was a long time ago." She looked up at him. "You know I had the biggest crush on you, even back then. I picked the dress I wore that night with you in mind. Not that you noticed..."

"Oh I noticed." 

She laughed again. "But really. I used to get excited when I ran into you at Bart's. I even told Rose I fancied someone at work. Didn't mention it was you."

"I had no idea."

"Oh come off it. I tried it on with you; do you not remember? I helped you solve a case then I asked you out for a drink. You literally said 'no' and left." 

He winced. "God. And yet you kept trying."

"Well I got you into bed in the end, so I guess I was onto something."

She leaned forward, looking over the edge of the balcony. The wind blended with the sound of whooshing cars in the distance as the rain danced on the pavement below. She turned back to Sherlock, glancing down at a box sitting in his hand. Her eyes darted between his face and the diamond ring that sat inside, her mouth dropping open as the facets glittered and reflected colours in the moonlight.

He stared at her, his face stern as he anxiously assessed her reaction. Then he realised he was still standing.

"Oh..." he said before getting down on one knee. He took a breath, preparing to speak.

"Sherlock," she breathed.

"Don't interrupt my train of thought," he replied, his tone snappier than he had meant it to be. "Sorry." He closed his eyes. "I'm sorry. Have I ruined it?"

"No! No, you... no."

"Okay." He took another breath. The damp floor was seeping through the knee of his trousers, but he didn't care. "My father calls my mother his 'better half'," he began. "I never understood why; I always thought it was some mushy term of endearment he used when 'wife' got boring. But now I get it."

Margaux stared down at him, her chest rising and falling heavily. She threw her hood down; it didn't matter that she would get wet, she needed to look at him properly.

"I do not feel whole unless I'm with you. You... are my better half. You have been for longer than I think I even realised." He brushed his soaking hair out of his face and wiped the rain out of his eyes with his sleeve. "When the world thought I was dead; when I... went away, there was not a day that I didn't think of you. I wondered what you were doing, if you were safe, happy, if you'd met someone and fallen in love, if you thought of me. I looked for your eyes in every sunset, your beauty in every... beautiful thing I saw. But when I came back... there was a little boy, and I got scared. So, I buried it – convinced myself I hadn't felt those things."

She bit her lip to stop it from trembling.

"I spent years keeping myself from you," he continued. "I wasted so much time and I will regret it for the rest of my life. I don't want to waste any more time."

She covered her mouth. "Oh my god," she said, her voice muffled by her hands.

"Margaux... Cave. Dr... Dr Margaux Cave," he huffed and shook his head. "Well I messed that up."

She laughed.

"Margaux, will you marry me?"

She dropped to her knees and threw her arms around him, squeezing him so tight he almost dropped the ring. She grabbed his cheeks and began to lay quick, urgent kisses across his face. He could feel her smiling as her lips met his.

He pulled away and slicked back her wet hair. "I believe John said you have to say yes or no."

"Yes! Yes."

He took out the ring, dropped the box to the floor and together, they slid it onto her finger.

She held out her hand, gazing at it in awe before looking back up to him. "You know what this means, don't you? I mean, you're absolutely sure–"

"Stop. Don't. Of course I'm sure."

"But Sherlock, you're going to have a wife. You're going to be someone's husband..."

"I'm not going to be someone's husband. I'm going to be your husband. That changes things entirely." He took her hands in his; she was shaking. "Are you nervous, or just cold?"

She dropped her head and breathed out a laugh. "Both."

*

Mrs Hudson was sat upright on the couch, her head tilted back and her mouth open as she slept. Sherlock nudged her awake gently. She looked around the room with bewilderment. 

"Mrs Hudson, you fell asleep." 

"Oh," she mumbled, glancing over his shoulder at Margaux. She leaned in close to his face. "Did you do it?" 

He nodded, giving her a slight smile. 

She squealed and jumped up, rushing over to Margaux and pulling her into a hug. 

"Oh congratulations, congratulations!" She pressed her cheek against hers, smiling so wide the corners of her mouth ached. "Let me see." 

Margaux held out her hand, the sight of the ring on her finger inciting butterflies in her stomach. "Right, I'm going to go and get dry," she finally said, hugging her again before making her way to the bedroom. 

Sherlock was standing in the kitchen with his hands on his hips. He didn't quite know what to do with himself.

"I'm so happy for you, Sherlock." 

"Thank you." 

"I've got champagne downstairs!"

"That's lovely, Mrs H, but it's 2am." 

"Oh," she laughed. "Of course." 

He rolled his shoulders, the dampness of his shirt sticking to his skin. He wandered slowly around the table, his excited landlady following him as she spoke. 

"We should have a party, don't you think? We could do it here!"

He turned around to face her. "Yes, I suppose we should."

"Nothing too crazy; just us, John, the kids. We could invite Molly, Greg, your mum and dad..."

He backed up into the doorway that separated the kitchen from the hallway, nodding politely.

Margaux emerged from the bedroom in a set of lace underwear and leaned against the doorframe. She cleared her throat, catching his attention with a smirk. His breath hitched as he laid eyes on her, before turning his attention back to Mrs Hudson in the kitchen.

"I could put on a little spread, tell everyone to dress up nice," she continued, oblivious to what was waiting for him down the hall.

"Yes, yes that all sounds excellent," he replied. "Really, I think you should plan whatever you want. I trust you, it'll be great."

"Really?"

"Yes! Whatever you want to do, let's do it. You only get engaged once! Well, most of us." His tone was overly enthusiastic. "Okay, goodnight!" he said chirpily before disappearing.

He rushed towards the bedroom, wrapping his arms around Margaux, hurrying her into the room and closing the door with his foot.

Mrs Hudson didn't seem to notice. Instead, she smiled, turned around and made her way back to her flat.

*

"Well... Do you like it?" asked John as he sat at the living room table.

The sun beamed through the windows. It was so bright, it was hard to believe that the country had been engulfed by storms just days before.

Sherlock sat in the chair beside him with his laptop on the table. He took an agonisingly slow sip of his tea as John waited for him to speak.

"'The man who has mastered the art of deduction has also mastered the art of seduction.' Really?" he finally replied.

"I thought that was clever."

"Well firstly, it's inaccurate; I did not seduce Margaux into accepting my proposal. Secondly..." He scrolled further down John's blog post. "'Sherlock has proven that as well as shooting holes in walls, he can also punch above his weight.'"

John snort-laughed. "It was a joke! I wrote plenty of nice things too! Like how I'm proud of you, how I feel privileged to have witnessed your relationship grow..."

"Mhm. How you... 'have great admiration for the woman brave enough to bind herself to Sherlock Holmes by law.'?"

John chuckled and shook his head. "Do you want me to fix it?"

"No, it's fine. You've already posted it now."

Rosie began to stir in her pram, waking from her nap with a soft cry. John unstrapped her and lifted her onto his lap, shushing her gently. He looked up at his friend and smiled. "I am happy for you, Sherlock. So... unbelievably happy."

Sherlock nodded, mumbling his response with a mouthful of tea. But behind his computer screen, he was smiling too.