A/N: Hey guys! So I posted a one shot titled "Rehab" a while back, and then I started to write this new fic and realized that Rehab would be a perfect prologue for it. I've changed the name, but if the first part looks familiar that's why. I hope that makes since. Anyways, I hope you'll like this new story, and let me know what you think. :)

8 Months Later

It Erin burst into Voight's office Monday morning. She couldn't take it anymore; she was going stir crazy sitting behind a desk day after day. She was a detective not a secretary, and she'd earned that title. Sure, she'd had screwed things up and made some mistakes, but she'd been punished, and she refused to suffer behind a desk any longer. "When are you going to give me a chance, Hank? I've done everything you've asked. I've been clean for eight months, and my ass has been in this precinct everyday. How am I supposed to regain your trust if all I do is answer phones and run errands all damn day? I need you to let me back out in the field. Give me a shot to prove it to you."

"Good morning to you too, Erin." He sarcastically replied. "How was your weekend?"

She sighed, her frustration bubbling. "It was fine. I went to a meeting, like usual. I went to the gym; I'm running ten miles now easily. I'm in shape, better shape than any of the guys you got out there right now. I feel good. I am good, and I'm ready to be out on the streets." She used his question as another way to sell her point.

"Have you been to the range?"

"Almost everyday. My shot has never been in question before, Voight. You know I'm good."

"Well, I've heard you, and I'll consider it." He nodded, but Erin was nearly positive her argument hadn't really reached him. "Now if you'd excuse me." He shooed her away as his phone began to ring.

"Please, Hank, at least think about it." She wasn't too proud to beg anymore. If she had to use their relationship outside of work as leverage, she would. With a last sigh, Erin turned on her heels and left his office. She knew she hadn't gotten through to him yet, but she was nowhere near ready to give up. She was determined to be working by the end of the week.

Voight's voice rang through the bullpen not even a half hour after she'd given him her spiel. "Lindsay." He gave her a simple nod telling her to follow him into his office, and she was sure her features gave away how stunned she was. Had she really convinced him to give her a chance?

She saw the file on his desk and was instantly disappointed. It was just her weekly drug test results. Hank had been making her get tested every week. She knew she didn't technically have to for work, but if it assured Hank that she was clean, she'd pee in a cup for as long as necessary. "I don't know why you call me in here for this anymore. We both know the results."

Hank ignored her statement and jumped straight to his agenda. "Vanessa Parker."

Her brows knitted together. This wasn't about her test results? The conversation was definitely taking a strange, rather puzzling twist. "Wh… What? Is that name supposed to mean something to me?"

"Illinois senator Gregory Parker's daughter." He offered more information.

The name became familiar. "So what does a young Chicago socialite have to do with me?"

"She was murdered last night in her 30 West Oak apartment. The commissioner just called and gave us the case. It hasn't hit the media yet, but you know when it does it'll be a shit show. We've gotta move quickly before the story gets out. You said you were ready? Well, this is your shot, kid."

Her eyes went wide. She wasn't expecting something this big for her first case back, but she was definitely not complaining. She did her best not to smile, after all a girl had died to make this possible, but regardless of how hard she tried, the corners of her mouth betrayed her. "I won't disappoint you, Voight. I'm ready for whatever. What's your plan?"

"Al's over with the family right now. Well, the mother and sister anyway. Dad's on a flight in from DC. They've all been cleared as suspects. The women have been in Toronto for the past week, and Parker was at the families' apartment in DC. All their stories check out."

"Do we have any leads then?"

"The family is working on a list of people that may have wanted Vanessa dead, or that may have done it as a way to get back at one of them. It's a politician's family, Erin. There's a lot swept under the rug, and a lot of skeletons waiting to be found. That's where you come in."

Erin anxiously looked around her apartment making sure she had gotten everything she needed. Voight had given her an hour to run home and pack before she'd be leaving to go undercover. The victim's younger sister, Madison Parker, was going to be introducing her cousin "Erin Parker" to the world in just a few short hours. Erin would be immersing herself fully into the lifestyle of Chicago's elite in order to get a better feel of what might have happened to Vanessa, solve the case, and prove herself to her boss.

In her few years in Intelligence, she had been undercover a few times, and it was normal for her to get nervous beforehand. Dry mouth, racing heart, sweaty palms were all the usual symptoms, but she could easily shove them away when it was time to get her head on straight. This time however, the nerves were near crippling. She had to prove she wasn't a liability, but an asset to the team. Her spot in intelligence depended on this mission going well, but that wasn't the only thing making her uneasy. These girls were infamous in the Chicago nightlife scene. Avoiding nightclubs, drugs, and alcohol wasn't going to be possible. She just hoped she was strong enough to resist the temptation when it was thrust in front of her face.

Standing in her doorway she flipped her sobriety chip between her fingers a few last times. She intended on leaving it at her apartment, but once it was time to leave she quickly shoved it into the front pocket of her bag. She didn't want to be left without it down the line. She had faith in herself, but a physical reminder of how far she had come these last few months was just extra encouragement.

When she arrived back at the precinct, everyone was frantically working to get everything set into motion for her stint. She made it to the doorway of Hank's office before noticing Jay was also in the room. Things had been tense between the partners as of late, but it didn't stop her eyes from scanning over his body, checking him out. Old habits die hard. It was then she noticed something peculiar. He wasn't wearing his usual jeans, in fact he had black dress pants on, and his usual leather jacket was replaced with a black suit coat. His new look completely baffled her until she noticed the duffle bag flung over his shoulder.

"You gotta be kidding me?" Her raspy voice questioned the two men that had yet to notice her. "Why the hell am I even here, Hank? I might as well be stuck behind the desk if you can't trust me to do this one thing!" His outfit had given him away; Jay was joining her undercover.

"Erin, your partner suggested you might not be ready to do this alone." Voight calmly responded.

Her anger was immediately redirected towards the fellow detective in the room. "You." Her head whipped toward Jay with a glare in her eyes.

Erin Lindsay's death glare was one no sane person would ever want to be on the receiving end of. Jay was not intimidated by much, but this look was scary. "Erin, I just don't want you going in alone. I don't think it's the right time."

"Nobody asked you!"

"Voight did!"

"Since when do you two talk about me? We both know you never had the balls to talk to him about me before."

"Erin that's enough." Voight interjected, but was ignored by the other two in the room.

"I'm doing what is best for the unit right now. You of all people should understand that." Jay fired back at her. If she was going to use their past against him, he'd throw in a dig too.

"I don't need a damn babysitter!"

"Nobody said you did. I'm your partner not your babysitter. We're equal here, Erin." He attempted to rationalize.

"Then as your equal, I'm saying I don't want you to come, and you should respect that."

"That's not how it works, Lindsay. You need backup, and unfortunately for you, I'm it."

"I'll be fine, Jay. Why do you even care so damn much?" Annoyance filled her tone.

"Don't ask questions you already know the answers to, Erin."

That's where he was wrong. She didn't know the answer anymore. Two weeks ago she was sure they were on the same page. She had promised him, that day in rehab, eight months ago, that she would get clean, earn back his trust, and then earn back his heart. She thought they had made it to that point. She believed he trusted her again, and thought he wanted her again, just as much as she wanted him, but then Thursday night had happened.

"Touchdown!" Erin threw her arms in the air celebrating victory from her cozy spot on Jay's couch. "How much do you owe me now, Halstead? Fifty bucks is it?"

"I only agreed to twenty!"

"Bullshit! The deal was fifty for whoever guessed closest to the final score, and you know it." She crawled over to his end of the couch and tried to fish his wallet from his front pocket.

"Hey, knock it off, Erin!" He laughed and attempted to stand and get away from her, but she wouldn't let him. Grabbing the back of his shirt, she pulled him back down into the couch cushions.

"Just give me my money and this wouldn't have to happen." She warned through laughs.

"I'll give you thirty. Deal?"

"Don't rip me off, Jay!" She swung a leg over his waist and pinned him beneath her. At this point, they were both laughing to hard for him to really fight back. She took his wrists loosely in one hand, while the other reached into his front pocket and took his wallet.

She was surprised and disappointed upon opening it. "Ten bucks. Are you kidding me?" She looked up at him, still perched on his lap. "You could have warned me you were broke before I went though all that work." She pouted sticking out her bottom lip. "I'm still taking the ten." Erin snatched the bill out of the wallet, shoved it in her back pocket, and tossed the empty leather wallet to the side.

She moved to get off his lap when she finally felt him beneath her. She took in a sharp gasp at the contact while Jay held back a groan. Instinctively, her eyes peered down at the little space between them. For the first time she thought about how her straddling his lap and digging around in his front pocket probably wasn't the smartest idea. It had definitely gotten him…excited.

"I'm sorry." He whispered an apology for his lack of restraint, compelling Erin to pull her gaze back up to his face.

Her breathing labored. She shouldn't have gotten turned on so quickly. She would have scolded herself had her thoughts not been completely preoccupied by all things Jay Halstead. Memories of him, his lips, his taste, his touch, his love muddled around in her mind, making the little hairs on the back of her neck and arms stand straight up. In that moment she wanted him, and it scared her just how much.

"Don't be." She wasn't sure words even came out when she attempted to whisper back. Her hands now somehow gripped the back of his neck, luring him in closer, until they met.

Timid and gentle their lips brushed, and then hungry and frantic they clashed. Tongue, and teeth, and lips, and desperation met in a flurry of fervent kisses. Lips on lips, lips on necks, and ears, and collarbones, and everywhere in between.

When she'd undone every button of his shirt she slid off his lap and onto her knees on the floor before him. Her nimble fingers worked at his belt as she panted for air. Just as she began to pass the leather through the buckle, his hands were on hers, halting her.

"Erin…" He was breathless too, but the way he said her name instantly communicated that something was wrong.

She peered up at him with eyes full of lust, and desire, and maybe even love, and it made the next few words even more difficult for him to say. Yet he said them anyway. "I can't."

It took a moment for her mind to catch up with his words, and when she did she wondered if she'd heard him correctly. It felt like a punch to the gut, and the heart, and every other part of her body. Was he really rejecting her?

He was the man that visited her in rehab, and held her hand and sat by her side when she didn't want to go to her meetings alone. The man that brought over chocolate milkshakes while the rest of the team went to Mollies after a hard shift. He told her she was strong and beautiful on the days where it was obvious she felt anything but. He was her best friend, and the man that had made her fall in love for the first time in her life, but suddenly it all felt so fake. Had he never really wanted them back together, but was just been trying to help make sure she stayed sober? Had he just changed his mind? Was he not falling with her, but just being a good friend and partner? Did she blur the lines and turn it into something it wasn't in her own head?

The thoughts and doubts and questions poured into her mind. She had to get away from him, fast, before the tears started. She rushed out of the apartment, ignoring his calls after her, and they'd barely spoken since.

The memory put a damper on her feisty mood. She didn't want to fight a losing battle anymore. Defeated, she gave in. "I thought at least you would believe in me. I guess I was wrong."

"Erin, you know I believe in you. It's just…"

She interrupted him. "You don't trust me. Jay, just say it. I'm not clueless. I'm an addict, not an idiot."

"Erin, I…"

"No it's fine. I've given you a reason to doubt me. It's just hard to accept that my own partner doesn't think I can get the job done. I can see I don't have a choice here, so lets just go" She shrugged sadly before exiting the office.

Jay stood behind feeling like the words biggest ass, but he was doing the right thing, wasn't he? Suddenly, he wasn't so sure.