It's not that she doesn't know it's wrong. Or inappropriate. Wildly inappropriate. She's well aware of that. But it's just that she can't seem to help herself these days.

That had been the theme lately.

No self control. No willpower.

It was sad, really.

Not that she's complaining. Not at all. Oh no, complaints were the last thing on her mind. Especially when Derek was doing his bendy thing. God, she loved the bendy thing. Even if it meant sneaking into the suffocatingly small, somewhat dirty on-call room shower. She doesn't care about anything at all when he does that. Nope. Nothing.

Not the fact that she has a consult in fifteen minutes. Not the fact that she can't hear her pager abandoned on the bunk bed.

And definitely not the fact that she is currently having dirty filthy secret sex with her ex-husband in the hospital shower.

She can worry about all that later.

"Shut up.", Meredith said, scrambling for her clothes.

"I didn't even say anything", Derek replied, a cocky, smug smile on his face. She watched him get into his boxer shorts and just for a second, just for one small second, let her eyes wander and was inevitably met with his sparkling blue eyes.

"I said, shut up.", he chuckled in response and began to button up his white shirt.

She's so late, so so late. The consult that was fifteen minutes is now barely, two minutes away and Bailey was going to kill her.

She reached for her lab coat on the floor and tried her best to avoid Derek's eyes.

"Okay, I'm gonna go and then you wait for a few minutes before leaving."

"I know the drill, Mer.", she moved toward the door, glancing back at him briefly, unable to resist.

"Have fun at your consult.", he wiggled his eyebrows advancing towards her, working on fixing his tie.

"Go away."

"Hmm, see you tonight, then?", he smirked, unhurriedly pressing a kiss to her neck, one hand resting on her waist.

"I am late.", his kisses were now travelling upwards, becoming more frantic. This would get out of hand very very quickly but damn it, if she didn't want to reach up to pull at his hair. She couldn't help the moan that left her only fuelling his actions as he pushed her into the door.

Screw it, she thought, grabbing his hair to pull his head back forcefully and bringing his lips to hers. His hands made their way under her scrub top as she pulled at his half-undone tie.

She shivered at his touch, his lithe fingers drawing circles on her abdomen. She could tell he understood from the way his hands tightened around her body. He'd spent years learning the ways of her body. What gave her pleasure, what made her tick, what made her lose her mind.

Which was probably why the sex was still so incredibly good. Even after four years of being divorced, he knew exactly how to make her come undone in a matter of minutes. Knew exactly how to make her feel so satisfied.

That was the only logical explanation for how she had found herself in this mess.

Or at least, that's what she liked to tell herself, anyway.

Derek reached to untie her scrub pants when her phone started blaring incessantly in her pocket.

"Peterson, what is it?", she hoped the intern couldn't hear her breathy sighs.

"I'll be right there.", Derek lifted her against the door, completely ignoring her declaration.

He pressed his body into hers and Meredith couldn't help the moan that left her as her legs tightened around his torso.

"I have to go."

"Your resident can wait.", he groaned, attempting to pull off her scrub top when she held his wrists, stopping him.

"Bailey can't.",she nudged him away from her body, landing on her feet dejectedly.

"Fine.", he replied putting space between them as he slowly moved backwards, dark blue irises fixed on her.

Damn it, he looked good with his shirt slightly undone, his silvering hair all tousled, his breathing ragged. Because of her.

A silent wave of pleasure passed through her at that knowledge and a sultry, stupid smile made its way to her face.

He returned her smile in earnest, blue eyes sparkling.

Ex-husband, she reminded herself quietly, making a beeline for the door.

"I'll see you!", he yelled after her.

Damn it, she really did hate it when he was right.

Derek's eyes flicked to the front door yet again, unable to help himself.

Stop it, she's not coming, he told himself.

For a second there when she'd been wrapped around him in that on-call room, Derek had been certain she'd show up. Certain that he had broken down all those carefully constructed walls she built. He'd been an expert at that, once upon a time.

But, turns out, ridiculously, surprisingly, he'd been given another chance to do just that.

A small, pleased smile spread across his face. Meredith tended to have that effect on him, anyway. Not just recently but, always.

Not just recently when they'd been sneaking around like teenagers. Making out in cars, having sex in the on-call rooms. It was as if they were at the very beginning again. Except this time the hiding wasn't from the Chief or her friends, this time it was from their children, their sisters, instead.

Oh, how times had changed.

Years ago, he would have never imagined this would be their life. But then, he would have never imagined they'd divorce either.

Or, that years later, they'd find their way back to each other in a disconcertingly similar manner. Not quite back, but perhaps closer to each other? He didn't know, the lines were so blurry and he was far too content to make any sudden moves to scare her.

He flipped through the pages in his hands, laptop open in front of him, attempting to focus.

The Parkison's trial was good, it was engaging, it should have kept his thoughts on track, yet his mind kept going back to that extra can of whipped cream he had picked up this morning. And how he could put it to exceptionally good use.

If she showed up.

And well, he couldn't ask her to.

They flirted, they had sex in hotel rooms in Minnesota, they sneaked into each other's respective homes but they didn't question, they didn't ask for things. It wasn't like that. This was easy. Simple. Uncomplicated. They'd done complicated. This was better. This was good. (and he was a very good liar)

Just as he was about to give up and head to bed, he heard a sound from his porch.

He headed towards it, opening the door, expecting some animal only to be met with the strangest sight.

"Meredith?", he whispered. She stood in the middle of his porch, a bottle of wine in one hand and what looked like a pen in the other, a small brown dog growling at her feet.

She looked up at her name, glancing at his confused self at the threshold.

What was she doing?

"This stupid yappy little dog hates me.", she twirled the pen in front of the stupid yappy little dog as if it was Harry Potter's wand only for him to let out an angry snarl in return.

"Shush, stop it.", she whisper-yelled, her eyebrows pinched.

A heady chuckle left him at her actions. He moved towards her, unable to resist.

"Hey, come here, Mr Whipple.", he whistled at the dog who instantly began to run circles around his legs.

"Why does he love you? ", she faced him, thrusting the bottle in his direction belligerently.

"Well, I happen to have that effect on people.", he raised his eyebrows at her, grinning widely. "And dogs."

She rolled her eyes, biting her lip, the mirth visible on her face.

"Whatever, McDreamy."

He laughed lightly at her words, eyes brimming with mischief.

"I thought you weren't going to see me tonight?", this time when she bit her lip, it made him want to slowly, thoroughly kiss her.

"Shut up. I hate you."

You love me, he almost said.

"Hmm.", his eyes caught her dark emerald irises, the same need mirroring his.

He moved closer to, reaching out to place one hand on her hip to gently pull her to him.

"Come on, let's go inside.", he felt her shiver at his touch, her breath smelling faintly of the wine in her hands.

"Bailey's asleep?", he'd already dropped Zola off at her sleepover.

"Yes. Snoring like a trucker.", Derek bent down to press a tender kiss to the angle of her mouth. Her hand made its way around his neck as a tiny, delicious moan left her.

"Snoring like his mother, I mean.", he finished breathlessly, interlacing their fingers.

"Ass.", she murmured playfully, grinning back at him as they headed inside hand in hand, the dog hot on their heels, nipping at her ankles.

She showed up.

Inexplicably, against all rules, Meredith had shown up.

And that small pleased smile on Derek's face? It had blossomed into a wide, radiant grin.

She had shown up.

Meredith curled up into him sighing contently.

Derek nuzzled her neck, breathing her in as she rubbed their feet together.

She should leave, she knew. She should have left after that first round. She should have never shown up, at all. This was dangerous territory.

Staying. Cuddling. They were sleeping together, not sleeping together.

But then there was the part of her that had shown up. The part that had made her go looking for a lavender-scented conditioner that she hadn't used in years when he'd mentioned in passing that he missed it.

The part of her that just felt so safe in his arms.

"I should go.", she mumbled into his hair.

Ask me to stay, she almost said.

He hummed non-committedly, his arm tightening around her.

Last year when Derek had bought this house four blocks from hers, she had never thought that it would aid them as dirty lovers. But here they were. Irrevocably tangled together, unable to let go. That's how it was with them. Complicated. Always so complicated.

But they were trying here. To uncomplicate it. Trying to make it simple.

"Okay.", he replied, propping himself up on his hand, catching her eyes.

So, she should go, now. He wanted her to, as well.

Except, if she could just-

Meredith crashed their lips together, thumb stroking his cheek lightly. They were both spent she knew that, this wouldn't go anywhere she knew that, too.

But she couldn't explain a lot of things these days.

Derek pulled her closer, deepening the kiss and flipping them until his body was steadily on top of hers.

Perhaps, he couldn't explain a lot of things these days, either.

"Or, you could stay.", he said between wet kisses down her neck, suckling delicately.

"Bailey will wonder why I'm here.", his arms flanked her face, fingers playing with her curls.

"We'll tell him you came over for breakfast.", he cocked his head at her and gave her a sleepy, spent smile.

"You look good in my shirt.", he beamed all of a sudden.

It was all the shirt's fault. She'd instinctively pulled it on after that toe curling whipped cream-infused second round. And now it made her never want to leave.

His stupid black Bowdoin shirt. All his shirt's fault. It smelled like him which meant that now she smelled like him.

And that made her feel so warm, and so safe.

Stupid stupid shirt.

"Okay.", she folded finally.

"Hmm.", he moved to her side, snuggling into her.

"But you better set the alarm for before he wakes up. And you make sure that I wake up and am decent before that."

"And you have to make me pancakes."

He let out a chuckle. "Yes, dear."

Stupid stupid words. Stupid sweet brain-man.

Casual, she reminded herself. It was just casual no strings attached meaningless sex with her ex-husband.

Just that.

She rested her head on his chest, distracting herself. "David wants us in the lab on Wednesday."

Derek yawned rubbing his eye. "Okay. I'll book the tickets in the morning."

"Back on Thursday?"

"Yes."

He picked up his phone from the nightstand, setting an alarm for six am. Only three hours, oh, she would regret this in the morning. She always regretted it in the morning.

"Right, alarm done. Setting a reminder to book flight tickets for…the twentieth."

"Not the twentieth.", she murmured stifling a yawn herself. The way he was rubbing her arm would put her to sleep very very quickly.

"You just said Wednesday."

"Wednesday's not the twentieth."

"Yes, it is, Mer."

"No, it's not."

"Meredith.", he replied resignedly, opening the calendar app and bringing it in front of her face. "See Wednesday- 20th of May."

That couldn't- that couldn't be right. Wednesday couldn't be the 20th.

It couldn't be.

Because then that would be mean, today was the 16th, or 17th really since it was past midnight.

But that- that couldn't be right. It wasn't. There must be something wrong with Derek's phone.

Meredith hurriedly lifted herself up from the bed, stretching out for her phone.

"Mer, what is it?"

Today is not the 17th, it is not, she repeated to herself.

Except in the glow of her cell phone, she was faced with the knowledge that it was, in fact, the seventeenth of May.

But that meant-

Crap. Crap. Crap.

Derek continued to gaze at her, perplexed.

She stood up to pace in front of the bed, her heart thumping rapidly.

This was not good. This was not part of the plan.

They were divorced. This was decidedly not uncomplicated.

"Meredith, stop, what happened?", he approached her, grabbing her arm gently to stop her oscillations.

No strings attached? Screw that. This was-this was like a freaking ball of yarn, there were that many strings attached.

"Derek.", she stopped, taking in a deep breath. His blue eyes glanced at her kindly, waiting.

She rubbed her face anxiously.

"If it is the 17th today, which it clearly is. It means that I'm late."

"Late? Late for what?", he asked, confusion apparent on his face.

"Six days. I am six days late, Derek."

A/N: hi, new story! This was definitely not part of the plan but wow here you go!

Accidental pregnancy has never been my preferred trope, to be honest but, this seemed kinda perfect. And fun.

And I wanted to write happy, funny, non-angsty MerDer- which is exactly what this fic will be.

Anyway, lemme know what you think, please! Would you be interested in reading more?

Thank you for reading!