Science and math. Those are the two things that have never let Katie down. It is part of who she is and helped her create her identity. It gave her purpose, goals and a career.

She has found she can apply science to nearly everything. Cooking is just the science of food. Shopping for clothes is all about knowing measurements and dimensions of your own body well enough to know what looks good on it. Even matching colors in clothing or home décor can be boiled down to science.

Katie even once spent an evening examining her own hair under a microscope so she could calculate the best hair care routine for her texture and type.

That she has the kind of time to spend on those experiments is the one place where science has failed her. She's yet to find the perfect formula for social relationships, if such a thing even exists.

People are too fickle with what they want or need out of other people. Attractiveness is subjective. It's impossible to turn it in to an equation.

This is exactly what was running through her head the day Stephanie walked in to the lab and said, "You know, I think my son has a little crush on you."

She should have laughed and said what a crazy idea that was, but instead she replied with, "What makes you say that?"

"Ever since you started tutoring him, you're all he talks about. How smart you are, how funny and so on. And when we found out who Joshua really was, he was more worried about your safety than his own sister's."

"Oh." Katie had known it from the start, that J.J. was constantly making puppy dog eyes in her direction. But hearing it from another source made it officially real. She laughed nervously and tried to shrug it off as she continued, "Well. That's totally inappropriate. I'll talk to him about it later."

"Don't worry about it. Having a crush on someone a lot older than you when you're a teenager is perfectly normal. I was in love with my biology teacher when I was his age, so I understand."

"Right, right. Of course. Wait… a lot older? I'm not old now, am I? How old is a lot older?"

Stephanie laughed and shook her head, "I'm sorry. I didn't mean anything by that. I just meant, you're an authority figure who isn't related to him, so it's all perfectly natural."

Katie sighed and nodded in understanding. The last guy she dated turned out to be a psycho with super powers and the only other person interested in her was about to be fifteen in a few weeks.

Instead of thinking about how she was going to talk to J.J. today, she was calculating how many cats she could conceivably take care of. Single cat lady was her destiny for sure.

"J.J., we need to talk about something –"

He didn't let her finish and reached in his backpack for a print-out that he quickly handed to her. "I know. I brought that article about genome engineering with me. The one I told you about. I was just going to e-mail it to you but I know how you like to make notes in the margins and corrections and stuff, so I printed it."

If a person's entire body could frown, that's exactly what hers just did. She even felt her eyebrows droop. "Thanks J.J., that's really sweet. But that's not what I wanted to talk about."

"Okay, then what?"

"I know about your crush. On me."

He instantly looked downward so that his hair was covering his face and she tried to imagine what shade of pink he had turned underneath. "Is it that obvious?"

"Your mom figured it out."

"Oh God…"

She reached a hand out towards him; first like she was going to pat his arm, then his shoulder and then she let it hover over his head before retreating without touching him. This was weird enough without her introducing physical contact.

"It's no big deal. Really. You just need to move on. And stop. Or something."

As soon as she said it, she realized how stupid it sounded. That was like telling her to stop liking oatmeal cookies. Feelings don't just go away in an instant, whether they're for people or cookies.

He lifted his head and looked at her like he also knew how wrong she really was. "You know, I'm not always going to be an awkward teenager."

"J.J. – don't…"

"Well, I might still be awkward, but the age thing is definitely going to change. And when that happens, what will it matter?"

She didn't have an answer for him so she straightened her posture and tried to look as authoritative as she possibly could. "It just does."

That was almost as bad as saying 'because I said so' and she knew she wasn't fooling J.J., not with his brainpower. "So does this mean you're not going to tutor me anymore?"

"Oh. No. Of course I'll still tutor you. I mean, who else is qualified? Besides maybe Reed Richards."

She laughed to break the tension and J.J. gave her a slight smile before looking back at book in front of him. Katie leaned a little forward and spoke in a more serious tone, "I do know Reed Richards isn't real, by the way."

J.J. laughed and nodded, "I know."

And just like that they went back to work, both trying to ignore just what happened. But it was hard to ignore entirely, especially with Katie making a concerted effort to keep distance between them physically.

It wasn't that she was bothered that J.J. had a crush on her. She was more bothered because it didn't bother her at all.

So time passed, as it tends to do, sometimes slowly and sometimes much too quickly.

She continued to tutor J.J., as she had promised, up until went off to college in Massachusetts when he was 17.

Some things got better, some things stayed the same. Katie got her doctorate and though they worked in the same lab, she was no longer Stephanie's assistant by the time J.J. went off to school.

Time ticked by and she could practically measure it in text messages, e-mails and school breaks. J.J. always kept in touch, sometimes on such a constant level that it was almost too much, and sometimes less frequently. But every time he accomplished something, Katie was one of the first to know.

J.J. grew taller and less awkward, more handsome and grown-up, but still as sweet as he had always been.

They never talked about who they were dating unless someone else brought it up. When she got invited to family dinners when J.J. was home, they both avoided spending time together without others around. Katie pretended (to no one but herself because no one else really noticed) that there wasn't a reason why, but she knew there was.

When J.J. transferred close to home to work on his graduate studies at CalTech, she knew that eventually she'd end up in some situation where they were alone together, whether by accident or design.

That time arrived nearly three weeks after he returned to California. It was definitely not by accident. It happened because J.J. knocked on her front door.

"J.J., what are you doing here?"

He looked down at her welcome mat and she suddenly felt very silly because it was covered in dancing kittens. "Can I come in?"

"Oh. Yeah. Of course. I'm sorry."

She stepped aside to let him in and he lifted his head as he walked by her. He stopped and gave her a shy smile as he watched her shut the door. He wasn't the same J.J. that she used to do math problems with. He was mature and confident, but still sweet and funny and thoughtful. Katie had only seen him a few times a year, but she had watched him grow up through those texts and e-mails that kept them tethered to each other.

"So. I'm twenty."

Katie pursed her eyebrows together in confusion. "I know. Your birthday was six weeks ago. I sent you that new Hawking biography."

"I know you know. But I didn't come here to discuss birthday gifts."

Katie didn't know if she should invite him to sit down or if they should just keep standing awkwardly in her entryway. She chose standing awkwardly while J.J. continued to explain his visit.

"You talk to me about everything. Work, the weather, the last TV show you watched or the last book you read. Sometimes you text me to tell me about a particularly good scone you got from the café on the corner. But you never tell me about who you're dating."

She pretended that her mouth wasn't going dry and replied quickly, "I'm not. I mean, not right now, but I was. I have. I still only have one cat so I'm not a lost cause yet. My Aunt Janet didn't meet her husband until she was 38, so you know, I still have time. And you… you have plenty of time. You're younger, so… so iso/i much younger."

"Would you stop that?"

"What?"

"I'm twenty now. That's what I came here to say. I know this thing between us was weird when I was fourteen, but I'm twenty now. I'm not a little kid anymore. It doesn't have to be weird anymore. I've read studies on relationships with age disparities, and guess what? They work. It doesn't have to be a big deal. If you want to be someone and they want to be with you, then you should just be with them."

Katie leaned against the wall behind her for stability and stared at him for a moment. "You've read studies? With actual science?"

J.J. grinned at her like he knew he had hit the right note. "Psychology, sociology, anthropology."

"Soft sciences."

"But still… science."

"Yeah, but…"

J.J. took a few steps closer to her and she realized she couldn't back away because she was already against the wall. She knew how many dates she had been on in the past five years and exactly how long it took for either her or the guy to decide it wasn't going to work. And she knew that exactly zero of those dates had made her feel like she did right now.

"Your pupils are dilated right now. That's science."

He was right. Of course he was right. That's why she didn't flinch at all when he leaned in and tentatively placed his lips on hers. J.J. had knocked on her door five minutes ago and now she was wondering why they hadn't done this immediately.

It was just like it was supposed to be, like you read about in books, but even better. It was slow at first, like he was making sure she wasn't going to freak out. There was no freaking out. She just leaned in and kissed him right back.

Her heart was pounding so loudly that if she had been paying attention she could have counted the beats per minute. Katie felt heat move through her and the kiss became more intense until she finally had to stop to breathe.

"J.J…"

He was just as breathless as she was but managed to reply quietly, "Yes?"

"I am going to have to take a look at those studies you talked about."

His eyebrows raised in surprise. "Right now?"

She answered with another kiss. Those studies could wait for another day, maybe even never. Because the one thing she had learned over the years was that science couldn't tell her how to feel.