Hello! This is my first attempt at a FanFiction! I know where I want this story to go, but any suggestions are more than welcome. Please leave a review and let me know what you think. Flashbacks are in italics. I am from England so some spellings may be slightly different. I tried to use the American version of words when I remembered! Please forgive any grammar mistakes.

Enjoy!

Chapter 1 – The Beginning

Erin Lindsay stood facing the door. She could hear the low sound of the TV from inside the apartment, but couldn't make out what was being said. She took a deep breath. What if this was the wrong move? What if this wasn't what he wanted? But, she reminded herself, he was the one who had suggested it. Well, implied it. She thought back to earlier that day. Her first case as a member of a federal task force had lead her right back to the Intelligence unit and her old team.

It was a hectic day and Erin was therefore surprised to find herself alone in the bullpen with her old partner, Jay Halstead. They made a few comments about the case as she walked around the front of her old desk and perched on the edge, facing Jay. Jay had made his way over to her as they'd been talking, finally stopping just in front of her.

He glanced quickly around, making sure they were alone, before taking another small step, a slight grin forming across his face. He was now closer to her than what would have been considered professional. As he moved in, Erin too glanced around before looking up at him from her position on the desk, her eyebrow slightly raised. They made eye contact and Erin felt her heart skip.

He was close enough for her to breathe in the soft scent of his aftershave, a scent that had become one of her favourites over the time they'd worked together. Jay looked down at her, his grin still in position.

"You know," Jay said in a low voice, his grin becoming wider. "We no longer work together. So a lot of the old rules, and regulations, they don't apply anymore."

Erin felt her heart rate increase as she understood what he was implying. They'd always said "Maybe one day." Well, maybe today was one day.

She held his gaze, feeling a half smile forming on her mouth. They remained there, him standing, her sitting, drinking each other in. She could feel the electricity between them, as she always did when they were close. It had been that way since the beginning and she knew he felt it too.

They were brought back to Earth as Agent Lang came up the stairs and started talking. Their heads snapped towards him, and Erin quickly removed herself from the desk. She made her way over to Lang and led him towards the interview room, giving Jay a meaningful look over her shoulder as she exited the room.

And now here she was, standing outside Jay's apartment. The task force wasn't like she'd thought it would be, and although they'd closed the case, she wasn't happy. She missed her old unit. The memory of the day swam in her head. She took another deep breath, and knocked on the door.

She held her breath as a few seconds passed. Then the door opened, revealing her former partner. "Hey," she said in a voice huskier than usual thanks to the stress of the day.

"Hey," he replied.

"Am I interrupting anything?" she said with a small smile.

"Err," Jay motioned to the TV, "just your own press conference. D'you wanna come in?"

"Yeah," she said, stepping over the threshold into his apartment and slowly made her way to behind his couch. "So this is how you're spending your evening?" she said, gesturing to the TV. "You must really miss me." He had joined her behind the couch and she turned to look at him.

"They didn't let you do any of the talking," Jay teased, and Erin let out a short breath of amusement. "No offence to Lang, but you're a little easier on the eyes."

She shook her head slightly as she looked at the TV. "It's not really my scene. Plus, y'know, Voight's got a rule. You never get your picture in the paper." Jay looked at her. He could tell something wasn't right.

"You wanna talk about your day?" He knew Erin was a private person and didn't like to show her vulnerability. But he was worried about her.

"Not really," she replied quickly, looking into his eyes. Her breath caught in her chest as she saw the emotion in his eyes. He really cared about her.

For the second time that day, Jay moved in closer, never breaking eye contact. He felt the familiar electricity between them as he saw the longing and need in her eyes. He slowly brought a hand up to her face, gently caressing her cheek and jawline. Her eyes flicked from his eyes to his lips, before holding his gaze again. He slowly leaned in and her face tilted up towards his.

They both closed their eyes as their lips finally met in a soft, gentle kiss.

Erin thought her heart might jump out of her chest. The feeling of his lips on hers was better than she could ever have imagined, and she had imagined it more times than she cared to admit. A warmth spread over her, starting where his lips met hers and reached the very tips of her fingers and toes. She knew then, no matter what happened with the task force, as long as she had Jay, everything would be alright.

They broke apart but remained close, pausing for the briefest of seconds to look at each other. They had just crossed the invisible line that they'd drawn when they had first started working together and decided it was best to keep things professional. Erin saw the burning passion and desire that was building inside her reflected in Jay's eyes, and thought "There's no going back now".

It was her turn to move forward, as she crashed her lips against Jay's. Her hands moved to his chest as she felt him return her kiss with equal passion and urgency. His tongue gently pressed against her bottom lip and she opened her mouth, granting him entry. Their tongues danced as Jay moved his hands to her back, pulling her further into him. He pushed her against the wall of his apartment, their mouths still joined. Jay felt as if every moment in his life had been leading up to this, and knew that he never wanted to kiss anyone else. This was right.

They broke apart again, the need for oxygen was too great. Their breathing was heavy as they once again stared at each other. Then Jay grasped her face and his tongue was exploring her mouth again. He pushed her jacket off her shoulders as she tugged on the t-shirt he was wearing. Her jacket fell to the floor as his hands moved to the buttons of her shirt. She dragged his t-shirt up and they momentarily broke apart as she pulled it over his head. They resumed their passion filled kiss as Erin's shirt met her discarded jacket on the floor.

Jay's hands roamed over her body, feeling the lace of her bra against his bare chest. She put her arms around his neck and entwined her fingers in his soft hair. Their breathing was heavy and their bodies burned with desire. Jay gently lifted Erin's body and she wrapped her legs around him, their tongues still entwined. Jay slowly carried her to his bedroom.

Panting, Jay rolled off Erin and onto his back. She moved closer to him as he covered their naked bodies with a sheet. She nestled into him, her head on his chest as his arm encircled her shoulders. She traced delicate patterns across his abs as he ran his fingers up and down her arm.

"Stay with me Erin," Jay whispered into her hair.

"Always," she whispered back.

Erin felt as if her whole world was shifting. She had never felt like this about anyone else, and she was terrified. She put thoughts of the real world out of her mind as she allowed herself to just enjoy the moment of being enclosed in Jay's strong, protective arms, and slowly drifted off to sleep.

Jay's initial delight at waking up the next morning after his and Erin's night of passion turned to anguish when she revealed that she was being sent on an undercover mission with the task force and could be gone for up to six months. He tried to be supportive, telling her he was happy for her, but Erin could see the disappointment and heart break in his eyes, telling her he didn't want her to leave.

If she was being honest with herself, she didn't want to leave either.

Erin was once again standing in front of Jay's apartment door. Had it only been last night that she stood in this same position, wondering what would happen if she knocked? She felt like she'd travelled a million miles since then. She knocked.

Jay glanced at the time on his phone. 10:45pm. Who would be visiting him at this time? He rose to his feet from the couch and walked to the door. He looked through the peephole and his heart skipped a beat. What was she doing here? Jay threw the door open.

"Hey," Erin said as Jay was revealed.

"Erin, what are you doing here? Shouldn't you be on a plane to Bolivia or something?" Jay questioned, confusion clouding his delight at the sight of her. "God, she's gorgeous," he thought to himself as she made her way into his apartment. She turned to look at him.

"I quit," Erin replied.

Jay didn't know what he'd been expecting, but it wasn't that. "Wait… What?" he managed to get out.

"I quit," she repeated. "It wasn't me, too much politics and red tape. Voight's given me my old job back."

"Wow." Jay ran a hand over the back of his head and through his hair, trying to take it all in. "So we're partners again." Jay was struggling to determine how he felt. He was elated that Erin wasn't leaving anymore, and that he'd still get to see her every day, but the thought of going back to a purely professional relationship was impossible to comprehend.

"Guess so," she smiled softly, understanding the conflict in his eyes. She reached down and took one of his hands in hers, entwining their fingers. "Jay, just because I'm back, it doesn't mean I wanna quit me and you."

Jay's heart leapt. Was she saying what he thought she was saying? Erin smiled at the astonished look on Jay's face, her dimples forming chasms in her cheeks. Jay loved her dimples.

Erin focussed on Jay's face, trying to gauge his reaction. She'd put it all out there, told him what she wanted. Sure, it'd be difficult. All the old reasons for not being together were still there. They worked together. Faced life and death situations together. And then there was Voight. But after the other night with Jay, and waking up in his arms, she didn't think she could cope if they had to return to their old relationship. She'd had a taste of what it would be like to be with Jay, and she wanted more.

Jay moved towards her, their fingers still entwined, and his signature grin spread across his face. "We're really gonna do this?" he asked, and relief washed over Erin as she grinned back. He bent his head down towards her and their lips met. Their kiss quickly became passionate and their hands roamed over each other's bodies as they collapsed onto the couch.

Soft sunlight was pouring in through the thin material that covered the windows, making the room glow gold. It was the morning after Erin had quit the task force, and after round one on the couch with Jay, they'd moved into his bedroom for round two. They'd eventually fallen asleep in each other's arms, feeling happier than either of them thought possible.

"So… How're we gonna play this?" Jay posed the question as he lay in bed with Erin curled up next to him. While Jay was fully on board with starting a romantic relationship with Erin, he was curious as to how she wanted to deal with it at work.

"Huh?" Erin had been in a world of her own, enjoying the feeling of comfort that Jay's arms gave, and thinking that she never wanted this moment to end.

"I said, how d'you wanna play this?" Jay repeated, inwardly finding it adorable that she was so content at that moment that she hadn't been paying attention. "I mean… are we gonna tell Voight or…" Jay trailed off. He really didn't want to spoil the moment, but they had to talk about it at some point.

Erin sat up, thinking. Jay repositioned himself, turning to face her, and levering himself up so his weight was supported by his bent arm as his elbow sank into the pillow. He could see the conflict Erin was feeling as he studied her face. He knew Voight was the closest thing she'd ever had to a proper parent and that he'd taken care of her when nobody else would. He wasn't sure if he'd ever know the full story, but he understood that Erin wanted to make Voight proud.

"Let's… let's just keep it quiet… for now," Erin hesitated, looking at Jay. It wasn't that she was ashamed of Jay, in fact, she wanted the world to know how happy he made her. It was just that she wasn't sure if she was ready for the commitment that came with announcing their relationship. She studied his face, trying to read his expression. "I mean, we could tell Voight, if you really want to…" she offered, "I just… I don't think I'm ready yet."

Jay looked at her. The morning sun was creating a golden haze around her slight figure, but he could see the worry in her eyes. He knew that Erin wouldn't enjoy lying to Voight, but he also knew how guarded she could be with her heart. He didn't want to jeopardise things by forcing her to admit their relationship before she was ready.

"I get it," he told her. "We'll take things slow and tell people when we're ready."

A smile spread across her face as she turned so Jay's chest was pressed against her back as they lay in bed. His arms wrapped around her as she softly whispered "thank you."

"Y'know, it might be kind of exciting… sneaking around," Jay grinned into her hair. His hands started to roam over her body.

"Oh yeah?" she teased seductively, arching an eyebrow as she turned so they were both facing each other again.

"Yeah," he teased back, his grin still in place.

Before she knew what was happening Jay had flipped Erin onto her back, causing her to shriek with laughter as he began to worship her body.

Erin grinned to herself as she made her way out of the elevator and to her apartment door. It was the weekend, so she'd spent the morning with Jay after agreeing to keep quiet about their relationship. She'd eventually had to tear herself away to take a shower and get a change of clothes. She smiled at the happiness she was feeling.

She turned her key in the lock and let herself into her apartment.

"Hey," Nadia called from her position at the breakfast bar. Nadia had been living with her since getting out of rehab so she could save up for an apartment of her own.

"Hey," Erin replied, dumping her keys on the table beside the door and hanging her jacket up. "Is that coffee?" she asked, indicating the mug in Nadia's hand.

"Yup, just made a pot." Nadia had a strange look on her face and was looking at Erin through narrowed eyes.

"What?" Erin asked as she reached for the coffee pot and poured herself a cup.

"So… who's the lucky guy?" Nadia teased.

Erin choked on the sip of coffee she'd just taken. "Wha... what?" she spluttered, looking at the grin on Nadia's face.

"Oh, I don't know…" Nadia began in a sarcastic tone. "That's just two nights in a row that you haven't made it home, so… who's the lucky guy."

"I don't know what you're talking about," Erin shot back, not making eye contact.

"Oh come off it Erin, you had a smile so big when you came through the door! Somebody must have done something right last night!"

"Nadia!" Erin exclaimed, wondering how she was going to get out of this conversation.

"Is it Halstead? Please tell me it's Halstead, you guys are so made for each other," Nadia pressed on.

Erin could feel herself beginning to blush and quickly turned away so Nadia wouldn't see.

"I'm not talking about this," Erin said lightly as she made her way towards her bedroom.

"Aha! So there is something to talk about!" Nadia squealed, spinning in her bar stool so she could watch Erin cross the room.

"I didn't say that!" Erin replied, still walking away. "I'm gonna take a shower now, okay?"

"I'm gonna find out who it is!" Nadia called after her as Erin disappeared into her bedroom. Nadia grinned to herself as she raised the coffee mug to her mouth, she enjoyed teasing Erin.

Thirty minutes later, Erin emerged from her room, her hair still damp from the shower. Nadia was in the same position at the breakfast bar, her back hunched over the massive textbook she was making notes from. She looked up at the sound of Erin's footsteps and turned to face her.

"Hey, you know I was only joking earlier," Nadia began. She didn't want Erin to think she was being nosey.

"Nadia, it's fine, honestly," Erin smiled at her. She enjoyed the fact that they were good enough friends now that Nadia could tease her.

"You don't have to tell me anything if you don't want to, but I'm here if you wanna talk," Nadia offered.

"I know, thanks," Erin replied, settling herself on the couch. She'd done a lot of thinking in the shower. She wasn't sure how she was going to keep her relationship with Jay a secret from Nadia, they did live together after all. And it would be nice to have someone to talk to.

"Hey," she called over to Nadia, who had returned to her studying. "You were right, earlier. I was with a guy."

Nadia shot off her barstool and bounded over to the couch where she knelt eagerly, her legs bent under her, facing Erin.

"I knew it! Tell me everything!" she squealed, before calming down and saying "y'know, if you want to."

"There's not much to tell," Erin offered. "We're gonna take things slow and just see what happens."

"So who is he? What's he like? Do I know him?"

"Uh… yeah… you know him," Erin said coyly, staring at her hands.

"Oh my gosh it is Halstead isn't it?!" Nadia exclaimed, smiling widely at the embarrassment on Erin's face.

"Yes, alright, it's Halstead," she finally admitted, feeling the heat rising in her cheeks.

"I'm so happy for you guys!" Nadia reassured her. "Anytime you want the apartment to yourself, you just say the word and I'm outta here for the evening. Just, y'know, let me know if I need to buy earplugs or something, we do share a wall after all!"

"Shut up!" Erin laughed.

"I've been rooting for you guys all along you know," Nadia smiled.

"Would you mind keeping it quiet for now, we don't want the guys at work to know yet, especially Voight."

"No problem, my lips are sealed." She looked at Erin who was deep in thought. "So are you guys gonna be able to keep it professional at work?"

"We have to, you know Voight's rule about in-house romances, and I can't lose Jay as a partner."

She fell back into her thoughts. Sure, it'd be a struggle, but they could do this, right? It would be just like going undercover. They would keep it professional at work, and when they were sure they could do it, they'd come clean to Voight. And he'd accept that they were together and let them remain as partners once he realised that their relationship didn't affect the job.

But something told her it might not be that easy. Voight would not be happy when he found out they'd kept it from him, and Erin shuddered at the thought of what he might do to Jay when he found out he hadn't "kept it in his pants."