A/N - Had this idea in my head for a while and just had to get it out. I hope you enjoy.

Chapter 1

Jay Halstead ran his hand through his hair as he sat at the bar. Downing the beer in front of him, he nodded to the bartender, pointed to the bottle in his hand and held up three fingers. The bartender's eyebrows rose slightly but he nodded and brought over three shot glasses.

This was why Jay had come to an anonymous bar this evening instead of the usual Molly's. On days like this, after cases like this, he didn't want to talk. In any case, Olinski and Antonio had already gone home, the cases with kids giving them a drive to head back to their families instead of to the nearest bar. Ruzek had disappeared with Burgess not long after and Jay had no desire to spend an evening making awkward conversation with Voight when all they both wanted was to get out of there.

Jay pushed $20 towards the bartender and shook his head at the offer of change. He ran his finger around the rim of the glass, deep in thought, until he heard someone clear their throat behind him.

"You waiting for anyone?" The woman nodded at the glasses in front of him, her voice husky.

Jay shook his head and gestured to the seat next to him, one of the few remaining at the bar. The woman smiled softly and sat down in the empty seat. The bartender appeared almost instantaneously and she grinned.

"I'll have what he's having," she smirked, holding up three fingers.

Her drinks arrived and she raised one in Jay's direction.

"To shitty Fridays?"

Jay smiled involuntarily and raised his glass in response.

"The shittiest," he replied, clinking the glasses together before they both downed the shot.

The girl grimaced slightly but seemed otherwise unaffected by the alcohol. She raised the next glass silently and Jay followed suit, the second quickly following the first. After a brief pause, she raised the last and looked directly at Jay.

"Erin."

"Jay," he replied, raising his final shot and knocking their glasses gently together before they both raised their glasses to their lips.

An hour later, the pair remained at the bar together, Jay's hand now firmly on the back of Erin's chair as she laughed at a story he was telling. The conversation had stayed light, neither party wanting to linger on their reasons for ending up there.

Erin looked at Jay, a recognisable look in her eye. She licked her lips slowly and Jay felt himself harden almost immediately. Erin smirked at him like she knew exactly what she'd done and Jay raised an eyebrow in response.

"I'll settle the tab?" Jay suggested, pulling his wallet from his pocket.

"I just need to visit the restroom," Erin replied, nodding. She walked off in the direction of the restrooms and looked over her shoulder just in time to catch Jay checking out her ass. She bit her lip whilst maintaining eye contact and Jay knew this was going to be a good night. He caught the eye of the bartender and left a wad of bills on the counter including a no doubt far too generous tip, but he didn't really care.

Erin returned from the restroom and walked over, scooping her coat up from the chair. Jay's hand came to rest on the small of her back and she smirked up at him once more.

"Shall we?"

Jay replied by guiding her out of the bar. As the cold Chicago air hit, Jay draped Erin's coat over her shoulders, taking care to run his fingers gently across her skin as he did so. Erin breathed in sharply and she looked up at Jay, her pupils wide.

Jay ran his thumb across her cheekbone and tilted her face upwards softly. She responded by leaning in, her eyes fluttering closed.

The kiss was everything Jay had imagined and more, her soft warm lips pressing gently yet insistently against his, her tongue flitting against his lips occasionally and he opened his mouth to her, happily obliging her unspoken request. His hand slipped inside her coat around to her back and he held her to him as the kiss deepened further, electricity seemingly pulsing between them.

When she pulled away, her cheeks were slightly flushed and her lips swollen. She looked up at him with a smirk that went straight to his crotch.

"Your place or mine?"

After a ten minute cab ride in which they'd failed to keep their hands off one another, they arrived at Jay's apartment. He opened the door and held it open for Erin to follow him in. He half expected her to look around but she only had eyes for him.

Flicking the door closed with her foot, she backed him up against it and kissed him once more, her hands slipping under his shirt as he divested her of her coat.

Before long, they were both shirtless and Jay slipped his hand into Erin's as he pulled her through his apartment towards his bedroom. She made quick work of Jay's belt and pants as they staggered towards the bed breathlessly.

Jay walked backwards to the bed and sat down as the edge of the bed hit the back of his knees. He brought Erin between his legs and undid the button on her jeans, sliding them down her mile-long legs before pulling her onto his lap. She shifted on his lap, rubbing herself against him and Jay let out a curse as he realised how good she felt.

He relieved her of her bra and brought his hands and mouth to her breasts, flicking his tongue around her already hard nipples. She moaned gently and bucked into him harder, her hands slipping into his hair. Jay rose from her breasts and attacked her mouth once more, nibbling on Erin's lower lip in a way he could tell she liked from how she shifted in his lap.

Without warning, he flipped her over onto her back and made his way down her body, lips and fingers trailing her skin as he did so. Slipping his fingers into the sides of her panties, he looked up to Erin for approval before he slid the lace garment down her legs and threw it to the side of the bed.

He trailed his fingers up her thigh and smiled as her legs instinctively fell open, allowing him access to her. She moaned softly as he ghosted his fingers over her centre and he felt himself harden more than he thought possible as he felt how wet she was for him.

He lay down next to her, one hand slipping into her hair as he pulled her to his lips once more, the fingers on the other hand rubbing circles around her clit, causing her to squirm next to him. He slipped one, then two fingers inside her, groaning at how tight she felt and imagining what she would feel like around his cock. She responded eagerly, her hands pulling at his boxers until they slid down his legs, her hand snaking around his cock and pulling at it slowly, her thumb rubbing slow circles around the head.

"Fuck, Erin, you're killing me," Jay moaned into her neck, his fingers pumping more insistently into her, rewarded by a tightening of breath and a small moan from the woman lying next to him.

Jay continued to pump his fingers in and out, his thumb coming to play with her clit as he did so and the ragged moan and the tightening around his fingers told him he was doing the right thing. He brought his head down to her breast and sucked on her nipple, continuing his ministrations and she snapped beneath him, her walls pulsating around his fingers and her breath coming out in desperate gasps. He slowed his fingers as she came down from her high and she looked to him, her face flushed and blissful.

"Fuck," Erin whispered. "That was… Fuck."

Jay replied by pulling her to him once more and the pair kissed once more, their tongues battling for dominance as Jay reached into the bedside drawer for a condom. He tore open the packet but Erin removed the condom from his hand as he went to put it on.

"Let me," she smiled, her husky voice causing Jay's cock to twitch uncontrollably. He groaned as she slipped the condom onto him, pumping her hand a couple of times as she did so.

Lifting her leg over Jay's body, she rubbed her centre against him as she leaned down to kiss him longingly. Rising once more, she directed Jay's cock and lowered herself onto him causing them both to moan simultaneously as sensation took over.

Erin moved her hips slowly at first, Jay hitting the point inside her that made her moan each time he thrust up. The movements became faster and Erin leant down to kiss Jay ferociously, her hands running through his hair as she moaned into his mouth. Jay clenched his jaw as he thrusted faster, trying to hold back the inevitable.

"I'm so close," Erin gasped, just as Jay reached his hand between them and found her clit once more with his thumb.

Erin came with a sharp intake of breath, her pulsing walls causing Jay to follow suit, his hand gripping Erin's hip tightly.

With a final few thrusts, the pair came to a halt and Erin came to rest on top of Jay, her head buried into his shoulder. They were both covered in a sheen of sweat, but that didn't stop Jay from trailing his fingers over Erin's back, reluctant to stop touching the woman on top of him.

"Wow," Jay said softly into Erin's ear.

"Wow," she whispered back, a smile creeping across her face.

It was fair to say that Detective Jay Halstead was distracted at work on Monday morning. He'd said a somewhat reluctant goodbye to Erin on Saturday morning after another round and the exchanging of numbers with a promise to call her. He rarely contacted one night stands again but there was something about Erin that gave him the impression he wouldn't be able to stay away.

The boys, especially Ruzek, had given him a ribbing when he came in with an unusually bright smile for a Monday but it hadn't bothered Jay. He just rolled his eyes and flipped them off when the boss wasn't looking, not that he would be likely to care.

Jay looked up as Voight came back into the office, back from downstairs where he had been retrieving the newest member of their team. Jay took a gulp of coffee as Voight walked through the office, glancing back down at his paperwork before looking up again and promptly choking on his coffee.

Voight looked at Jay with a mixture of disgust and distain as he saw what, or rather who, he was looking at.

"Halstead," he barked. "Keep your eyes in your sockets."

Jay coughed and spluttered as he looked from his commanding officer to the new detective and back again.

"Everyone," Voight announced. "This is Detective Erin Lindsay, the newest member of Intelligence. She'll be partnering Halstead."

Various welcomes came from around the room but Jay didn't say a word as his eyes stayed on the new detective, the woman from Saturday night, Erin Lindsay. She looked back at him, a similar look of surprise, albeit not the sheer panic that Jay was sure he was displaying, on her face.

Voight marched towards his office, a mug of coffee in hand. Just before he reached the door he turned to Jay and cleared his throat.

"Halstead?" He barked again. "Off limits. You understand me?"

Jay nodded. This new partner situation could turn out to be a lot more difficult than he had imagined.

A/N - Please let me know what you thought. This was my first time writing any M rated stuff so hopefully it wasn't complete crap. I will try and update this as often as I can but I can be pretty slow when it comes to updating things... Also, I tried to keep things as American as I could, but I'm English so some words may not be Americanised, my apologies for that.