Disclaimer: I do not own any of the characters from How I Met Your Mother, just the story.

A/n: First HIMYM fic, reviews are super appreciated!

Chapter 1

It was a day like any other in McLaren's Pub (or so they thought). The five friends were hanging out, drinking some beers and having one of their usual heated debates over something most people would consider stupid but to them it was important. The hours passed and one by one they threw in the towel and went home. A tipsy Lily came back from the bathroom to tell her husband she had enough and was ready to go home. Marshall sighed and looked at his wife with puppy dog eyes suggesting they stay a bit longer. Lily knew this week had been extremely stressful for him at work and these nights out with their friends meant a lot to Marshall and helped him unwind. She chuckled. "Alright, baby. You stay, but not too long!." She turned to her friend and raised an eyebrow at her "Robin, take care of him for me." and said goodbye to her. Marshall, ever the gentleman and great husband he was, called his wife a cab and personally paid and gave instructions to the cab driver to make sure his wife got home safe.

And then there were two.

Marshall sat back in the booth with two more beers and two shots of tequila. hanging with Robin was never awkward or weird, even though she was a woman. It felt normal, like he was talking to one of the guys. A very attractive guy, at that, but he felt more than comfortable nonetheless. The beers and shots kept coming one after the other and when they were considerably buzzed, words really started flowing.

-"He buddy, shouldn't you be going home soon? The ol' ball and chain is waiting for you, brah." She teased mockingly.

-"Ah, let her wait. Whatever."

Robin looked shocked for a moment. Marshall never talked like that about Lily, they were always so lovey dovey with each other. Sometimes they made her want to puke.

-"Whoa. Were did that come from?!"

-"Lily and I... haven't exactly been on the best of terms lately. We're kind of having some problems."

Her eyes narrowed and she had a very confused and curious look on her face. He paused for a moment and sighed.

-"I have to tell you something. I'm not so sure I should say anything to anybody, least of all you, but I just... have to."

Robin's eyes widened and she suddenly became nervous. What was so important? She was so anxious to hear what Marshall desperately had to say that she couldn't even manage to ask what it was. She just kept quiet and very attentively waited while she took another sip of her beer.

-"Lily and I haven't had sex in six months."

Robin spit out her beer "SIX months?! Marshall, what the hell? You guys bang like, everyday. What happened?"

-"Well, that's the thing. Nothing actually happened. Well... kind of..."

-"Okay, buddy, you're losing me here. Did something happen yes or no?"

Marshall sighed deeply and took a large chug of beer.

-"Okay. Here's what happened. Six months ago I kinda' had a dream. And, uh, ever since she feels weird and threatened or something. Mostly just uncomfortable, I guess. See, thing is, it was a sex dream... it, uh... it was about you."

He stared at the table for what seemed like several minutes but were actually seconds. He couldn't look up at her. She was just staring at him blankly, what the fuck? Finally he snapped "Well, say something, Robin! Jesus."

-"Okay! Okay! Damn, give a girl a moment..." Robin was quiet again for a bit. She wanted to get her thoughts together first, she wanted to say the right thing and not just blurt out the first thing that came to her mind. Maybe it was all the alcohol in her system, or the fact that she had always found Marshall kind of sexy but refused to see him in any sexual way because she really valued her friendship with Lily. In any case, she needed to think before speaking because the first thought on her mind when he heard the words come out of his mouth had been "Huh. That's... sexy."

In spite of this, she managed to compose herself. "Well, Marshall, what's the big deal? It's just a dream, it's not like it actually happened." Sounds tempting, though... "I mean, what's her problem?"

Marshall looked relieved. "That's exactly what I said. What's the big deal? It was a dream, it can happen to anyone and it meant nothing. It's no biggie but she didn't exactly take it that way. She said that it was a big thing because you are our friend and because of... nevermind. She just... took it hard."

-"Marshall! What?! I'm beginning to hit my limit here."

He sighed yet again and ran his hands through his hair. "Well... she, uh, she said that it's a big deal because of the thing. Because of our, you know... sexual platonic thing."

-"What the hell are you talking about? What sexual platonic thing? There's no sexual platonic thing... Is there?"

-"Well, you know about The Mermaid Theory, don't you?"

She snorted and started laughing. "That is just another one of Barney's stupid, ridiculous theories that are never accurate or true. Please don't tell me you actually believe it, it's bullshit."

-"Excuse me. Barney's theories while certainly far fetched have proven to be -on more than one occasion- extremely true. And The Mermaid Theory just happens to be one of them."

-"Oh, okay, Marshall. So before because I was more Lily's friend than yours, you thought of me as something else and now all of the sudden I became a mermaid and you find me attractive?"

-"In a nutshell, yes. You were a manatee, now you're a mermaid. Case closed, it is what it is. Boom. Mermaid Theory."

-"So... like, you're attracted to me? You think I'm attractive?"

Marshall heard the smugness mixed with excitement in her voice. He felt a little awkward now, like he had just entered a place he really wasn't supposed to. "Uh. well... you know, you're uh... you're okay."

Robin scoffed. "Excuse me? I'm okay? Dude, you just said I'm a mermaid. Mermaid's are hot, therefore so am I. Yup. Lawyered."

-"Please. You can't say 'lawyered' without my consent. Everybody knows that."

Robin was exasperated and excited at the same time. She loved arguing with Marshall, it was always so much fun. Especially about this! "Don't change the subject! You-"

Marshall interrupted before she could finish talking. "Alright, yes! I think you're hot, you're extremely attractive and sexy. You know this. Happy now?!"

Robin's jaw dropped. It's not what he said, it's how he said it. Like he'd been waiting to tell her all along, like he couldn't wait another minute to blurt it out. It was... hot. She was indeed happy.

-"Wow. Thanks." She said smugly with a huge grin on her face as she took another sip of beer.

Marshall rolled his eyes at her, turned around and ordered two more shots of tequila. It was imperative. "You can wipe that smug smile of your face Miss Thang.", he teased.

She laughed, clicked her beer to his and said "Cheers! To The Mermaid Theory." They both smiled and drank. She looked at him in a peculiar flirty way that he had seen before, but never directed at him.

-"You know, you're not so bad either Marsh."

-"Oh, really? Am I a mermaid, Robin?" he said teasingly.

-"A merman. You know, one of those hunks but without the abs."

-"Oh, well thanks a lot!"

She chuckled and looked at him in that same way again "It's good, though. Cuddly and strong... and big. Yeah, you're not bad at all."

Marshall smiled and looked down in that irresistibly shy way of his. He looked back up and stared at her for a moment, thinking how very sexy she looked with that twinkle in her eye. What's a little flirting? No biggie.

They both had a couple more shots and beers before they finally decided to head home. they had engaged in that mild flirtation the rest of the night, but all the while making the occasional joke to lighten the mood a bit and remind themselves that it was just that. A harmless flirtation.

Marshall may have been drunk, but the gentleman trait stuck with him. They both hopped into a cab and told the driver to head first to Robin's because he wanted to make sure she was safe home. In the cab drive they were mostly quiet. Strangely, they felt different. Maybe it was the fact that they had been sitting in a stuffy bar drinking all night and getting up made their drunkenness more palpable. Maybe it was the fact that they were so close to each other in the back seat of that cab... Whatever it was, suddenly the air felt charged and the space between them smaller. Much smaller.

A few minutes before making their first stop the car hit a huge bump on the road. The sudden movement made Robin fly a bit out of her seat and land back down harshly, dropping her side on Marshall's lap. He held her tight to help her get up and suddenly they were face to face, inches away from each other and their eyes locked on one another. They looked at each other with longing, each examining the other's stare and mouth and their breathing faltered a little. Finally, they arrived at Robin's place. They're eyes stopped meeting when the driver said "We're here.". Robin cleared her throat. "Right. Um, okay. Well, I'll see you tomorrow then, Marshall. Thank you for making sure I got home okay. And for, uh... everything."

She turned to open the door and as soon as she put her hand on the door handle, she suddenly and abruptly felt an impulse, an urge that she couldn't control. She turned back around, grabbed Marshall's face and kissed him fiercely. Marshall stayed petrified for a second before he instinctively started kissing her back. They broke the kiss when Robin, fueled by his obvious desire for her bit his bottom lip. He let out a soft moan that almost made her take her panties off right then and there. Marshall pushed her back by her shoulders and reached into his back pocket to pull out his wallet. He got out a $20 bill, threw it at the front seat without breaking his gaze at Robin and said "Yeah, there's only gonna be one stop."

She grinned and they both stepped eagerly out of the car. As they were making their way upstairs Marshall grabbed Robin's waist from behind her and pulled her body to his. He hugged her and gently brushed her raven hair away from her right ear. He trailed kisses from her ear lobe down to her neck. Robin threw her head back and closed her eyes, marveling in the amazing sensation. She opened her eyes, kissed him and grabbed his hand to lead the way to the apartment. She couldn't wait any longer.

As soon as they went inside, Marshall closed the door shot by pushing Robin against it. They kissed each other with so much desire and passion. In that same way they headed to Robin's room where they continued their heated encounter on the bed. Hours passed, but they didn't notice. They were completely lost in each other. Finally, they wore each other down and drifted to sleep.

Marshall opened his eyes. He had a slight headache. Damn tequila. But other than that, he felt great. Amazing, actually. He looked to his right and saw Robin sleeping right next to him. She was sleeping on her back with the pearly white sheet covering up just below her waist, around her hips. He admired her beautiful skin and shape for a moment and though about how very peaceful she looked. She looked beautiful. His eyes widened as if he was just now realizing the gravity of what happened. Oh my God, I'm in Robin's bed. He turned to his other side to find his pants hanging from the side table. He reached in his pocket and grabbed his cellphone. Thirteen missed calls and various messages. Oh, shit...