Four months earlier…

"This was a bad idea." Temperance Brennan muttered to herself as she stood in the hallway outside her partner's apartment with her suitcase at her feet.

It was the day after Christmas and she should have been on a plane to Peru to examine the 1500-year-old skeletons found at an ancient ceremonial site, but instead, she was here. Still in DC. She had postponed the trip once already to have Christmas with her father and her brother while they were in prison, and now, it looked like she was postponing it again.

She had set off in a taxi to the airport but for a reason she wasn't entirely sure of, about halfway into the journey, she had asked the driver to turn around and take her to Booth's apartment instead and now here she was, outside his door, uncertain of what she hoped to achieve by coming here.

Feeling nervous, suddenly worried that this wasn't just a bad idea, but a terrible idea, she inhaled a shaky breath and raised her hand to knock on the door before she could change her mind. It took Booth a while to answer the door and Brennan panicked for a moment thinking that maybe he wasn't back yet after taking Parker to Vermont. A few moments later though, Booth opened the door, and when he saw that it was Brennan waiting on the other side, he smiled widely, clearly happy to see her.

"Hey Bones! What're you doing here? Shouldn't you be on your way to Peru?"

Booth was clearly not expecting company. He was dressed in old grey sweatpants, a black graphic tee, and slippers. Brennan could also hear music from what sounded like a classic movie coming from the TV. He still had his Christmas tree up and it looked exactly like the one he and Parker had brought to the prison trailer as a Christmas gift for Brennan and her family. She felt a smile creep across her face as she became momentarily transfixed by the lights that were twinkling like tiny stars in the dim light of late afternoon.

"Can I come in?" She asked as she tore her gaze away from the tree.

"Sure!" He stepped back and she entered the apartment, wheeling her case behind her.

"I was worried you might not be back from Vermont yet." Brennan said, voicing the concern that had only surfaced once she had been stood at his door.

Booth rubbed the back of his neck and Brennan noticed his stiff posture indicating his back was causing him some discomfort. "Yeah, I only got back about an hour ago. I drove him out there last night then I pretty much drove straight back. I only stopped to sleep in the car for an hour or two and for some breakfast so I'm pretty tired."

Brennan was beginning to doubt that now was the right time to be here with him being so tired and all but before she could say anything, Booth noticed her suitcase and raised an eyebrow at her quizzically. "Did you miss your flight or somethin'?"

Brennan hesitated, uncertain of how to answer his question when she wasn't sure why she was here herself. "Yes. Sort of. I…"

Booth raised his eyebrows at her evasive reply. It was a simple question, and it was unlike Bones not to give a direct answer.

Brennan hesitated. How could she explain it to him without sounding like she had lost her mind? All she knew was that since they kissed in her office, she hadn't been able to stop thinking about him. She was aware of how much affection she had for Booth, and she had always assumed it was simply because they were such close friends. But now, she wasn't so sure. The kiss had not only intensified that affection, but it had also triggered a feeling inside her that she hadn't experienced before. It was only meant to be a fulfilment of a bribe to satisfy Caroline Julien's puckish tendencies so Brennan could spend Christmas with Max and Russ, but it had ended up being so much more. The kiss hadn't been as sexless as Brennan had proclaimed it to be and at first, she thought maybe it had been because she had finally been able to act upon her secret attraction to her partner. That it was just unreleased sexual tension that had made the kiss so intense. But when she couldn't stop replaying it in her mind afterward, she thought that maybe it wasn't that at all. Then, when he had given her the best, most thoughtful Christmas gift ever by showing up outside the prison trailer with that Christmas tree, she had felt it again, only stronger and she needed to know why.

Since then, a conversation she'd had with Angela months ago had been replaying in her head. They had been talking about love and relationships and Brennan had told Angela that she knew that sharing a strong emotional attachment with another person can be a good thing, but there was a disconnect between her mind and her emotions. Brennan had explained that she always felt the need to posit the potential problems, to calculate the probabilities of success and failure. Angela had told her that she understood that she gets scared. But also, she misses out on so much, and so does the person she is keeping herself from. Brennan couldn't help but wonder, was she keeping herself from Booth? They already had that strong emotional attachment, Sweets had told them so even if it hadn't been obvious to Brennan already. Would it be so scary to take that attachment one step further? Is that what these feelings were? Had the kiss triggered a deeper emotional connection between them?

Brennan eventually came to the conclusion that in order to test her hypothesis, she needed to kiss Booth again to see if it felt the same, to make sure she wasn't imagining this new feeling of a deeper connection that was thrumming in her veins, that she seemed to be powerless to resist. That was the reason she was here, she realised.

She released her grip on her case and before she could change her mind, stepped towards Booth. Just like when they kissed in her office, she took a hold of him. As he wasn't wearing a jacket, she couldn't grab his lapels, so instead she grasped a handful of his T-shirt and pulled him toward her. She briefly saw the confusion in his chocolate brown eyes before her eyelids slid closed and she pressed her lips to his. He hesitated for only a moment before she felt him relax into her and returned her kiss with fervour, his tongue teasing her lips before sliding into her mouth when she gasped in pleasure. Brennan tightened her grip on his shirt and Booth's hands found their way to her waist, his hold on her firm yet gentle.

They kissed passionately until Brennan drew back, her cheeks flushed and a small smile on her lips, her theory tested and her curiosity satisfied. It didn't feel the same as last time. It felt even better.

"What was that for Bones?" Booth asked, breathless. He raised his eyes to the ceiling, he didn't remember hanging mistletoe in his apartment, but there must be some up there – it was the only explanation.

Brennan simply smiled and kissed him again. She placed her hands on his chest and pushed him, forcing him to walk backwards as they kissed until the backs of his knees touched the couch. He sank down, pulling her down with him so she was straddling his thighs, not wanting to end this moment or to question what was happening between them. They continued to make out, their hands roaming, exploring, for a long time before Brennan's hand inching toward his crotch made Booth suddenly come to his senses. Trying to restore his equilibrium, he sat up and shifted Brennan from his lap, putting a little distance between them. She was intoxicating and he needed to keep a clear head to make sure they didn't rush headlong into something they would both regret.

"What's going on here Bones? Why are you doing this?"

She hid it well, but Booth could see the hurt in her clear blue eyes as he questioned her motives for her actions these past twenty minutes.

Brennan felt a twinge of anguish when Booth queried her behaviour and she had to fight to quell the feeling of rejection that was threatening to force its way to the surface. She knew her actions were incongruent with her usual demeanour which made her want to resort to her practiced response that she was simply satisfying her biological urges to avoid the difficult explanation he would no doubt expect. But that would have been a lie, and she would want him to be honest with her if the situation was reversed so she knew she should be honest with him. No matter how difficult it was for her to describe the feelings and reasons behind her actions.

"When we kissed under the mistletoe, I felt… something. A change in how I feel about you. I've never experienced it before, and I can't explain it or rationalise it. I have been unable to stop thinking about it since and when I was on my way to the airport, I realised I couldn't leave without trying to resolve it, to assess if the feeling would be replicated if I kissed you again."

Booth was surprised by her response. He was expecting some of her usual crap about hormones or 'biological urges' or whatever, but not this. She felt something? A change in how she feels?

"What kind of 'something' did you feel, Bones? I mean, was it good or… bad?" He cringed when he considered that maybe she was trying to ascertain for certain that she simply wasn't attracted to him and never would be.

Brennan paused trying to find the pertinent words to describe how she felt. In the end, she settled for honesty again.

"It was good… but I can't describe it Booth. I have experienced lust and desire on multiple occasions, but this felt different. It felt more profound than that. It felt like a deepening of our existing connection, and yet still more at the same time. All I know is, it feels intense and irresistible."

Booth felt like his heart skipped several beats and hope swelled in his chest at her description of her feelings. Could it be that the impossible was happening? Was Bones falling in love with him?

"And when we, y'know, kissed again, did you still feel it?" Booth tried but failed to keep the hope out of his voice.

She smiled that cute little half smile that he loved. The one where just one side of her mouth quirked up and brought out the dimples in her cheeks.

"Yes. Even more than the first time, and I would very much like to do it again."

Her voice was low and sultry, and Booth knew exactly what she meant about what she felt being irresistible because he felt the exact same way. She gasped with joyful surprise when he pulled her back onto his lap, threading his hands into her soft auburn hair and pulling her full lips to his, his tongue tasting, teasing, enjoying each movement, each touch. Her hands roamed his torso before eventually pushing his T-shirt up over his sculpted abdominal and pectoral muscles, encouraging him to remove it. He pulled his T-shirt off over his head then, pushed her jacket off her shoulders before his fingers began to eagerly work the buttons on her blouse.

Somehow, without either of them being consciously aware of it, they found their way to the bedroom, leaving a trail of clothing behind them as they undressed each other.

Brennan hadn't expected intercourse to be the outcome of coming here tonight and she kept anticipating the moment where she might begin to regret what they were doing or for it to feel abnormal, embarrassing even to be doing something so intimate with someone that she had worked with almost everyday for the past three years. But that moment never came. It felt so natural. Like this had been a part of what they were all along.

Every touch, every kiss was instinctive, satisfying this new craving for him and Brennan got a first-hand demonstration of what Booth had meant when he had explained the difference between crappy sex and what he had described as the real thing. As they lay in each other's arms afterwards, satisfied and replete, Brennan knew she had gotten herself into a highly complex situation, one that she unexpectedly had no desire to get out of.

It went against everything she had ever believed in, but Brennan found herself falling in love, hard and fast, in a way she had never anticipated. She'd heard people talk about love, read descriptions in literature, and investigated the science behind it. But none of it had prepared her for how it would feel to experience it herself. Particularly when she had always believed that it didn't really exist, that it was all just hormones and chemical reactions. But she couldn't deny now that there was something more to love than just chemicals. That feeling she experienced that prompted her to seek Booth out just to find out if the feeling could be real, never went away. It simply intensified until she felt like they were bound together by an invisible force, like they really were two halves of a whole, working together for the common goal of simply loving each other and making each other happy.

They decided the morning after that first night together that they were going to keep their new relationship status a secret. No one could know. They knew that with Dr Lance Sweets - the young FBI psychologist - constantly sniffing around their pairing that any change in their relationship that he deemed a negative one could spell the end of their partnership. Something which they both wanted to avoid. Their partnership was one of the best things to happen to both of them and to be separated would be a huge blow both personally and professionally.

They both found keeping their secret difficult to begin with, but unexpectedly, Brennan found it particularly challenging. Booth saw how troublesome it was for her when they were together at work to keep her behaviour towards him the same as it was before. So, he suggested that they treat it as if they were undercover. Only, they were undercover as themselves, their former selves. It made sense to Brennan and she slipped into the role easily. While they were at work, they maintained their usual, professional demeanours. Even when they were alone together in the car or in Booth's office, they restrained themselves so it didn't make it harder to slip back into character.

In the evenings and on weekends though, they were just like any other couple. They went on dates, spent time at each other's apartments, and had a lot of sex. They were happy. Brennan delighting in this discovery of love, and Booth not able to believe his luck that his beautiful partner, who he had been in love with for 3 long years and had never been able to act upon it, was now not only able to tell her how he felt but know that she felt the same way.

Weeks turned into months, and, as far as each of them knew, nobody suspected anything had changed between them at all. Even through challenging cases and her father's trial, which had been difficult for both of them, they had maintained their cover. That all changed though during the case where the wannabe singer Tommy Sour's body was found in a field of Johnson grass. The issue wasn't with the case itself, but with what turned out to be the victim's stalker. Pam Nunan had immediately assumed Booth and Brennan were a couple, a claim which they had rebuked. But when Pam began to display possessive behaviour towards Booth, Brennan thought that telling her might make her back off. However, Booth thought it might provoke her even further and she probably wouldn't hesitate to report them to the FBI too.

Brennan conceded that he was probably right, but she felt uncomfortable about the situation. She had never felt possessive towards any of her previous sexual partners, but Booth meant more to her than the sum of all those men combined, and she felt an irrational need to protect him from this woman who Brennan was convinced was psychotic.

Brennan just never could have imagined that she would be proven right in the most devastating way. That night at the bar when Pam shot Booth, Brennan had failed to protect her partner, her lover, the man who had given her so many things that she hadn't even realised she was without. That bullet was meant for her. Brennan would have taken a thousand bullets if it meant that Booth didn't take the one for her that ended his life.

That night, Pam Nunan hadn't just taken the life of Seeley Booth, she had taken a large portion of Temperance Brennan's life too. In the blink of an eye, a huge void had been torn into Brennan's life and she knew that even if she lived for another 100 years, it would never be filled.