(A/N): A cute, fluffy little oneshot because I am fuming still over that episode I've just watched. In my head, Jack and Nikki still have regular contact with Rosie. I own nothing.

Rosie.

Simone blinked in surprise as she rounded the doorway to the office area, finding Jack in his office chair like usual, but it wasn't Nikki occupying the opposite chair. Instead, a teenaged girl with mousy brown hair tied back in a ponytail sat in the seat, twisting from side to side slightly as she laughed at something Jack had said. Simone paused for a moment, watching the easy atmosphere with a furrowed brow, trying to work out who the newcomer was and how she fitted in to the odd dynamic of the Lyell.

"If you break that chair, I'm not covering for you." Jack grinned, shaking his head as Rosie swivelled round on Nikki's desk chair once again. He and Nikki spoke to Rosie every week and took her kite flying once a month when the weather permitted. More recently though, Julia, Rosie's mum, had taken to asking Nikki and Jack to be something of a babysitting service for the teenager. Rosie had rolled her eyes at her mum's suggestion, but she didn't mind spending a little time at the lab before sleeping in Nikki's spare room for a night here and there. It had been strange and awkward at first, for all of them, but they'd settled into a new routine, as strange as that sounded.

"And here I thought we were friends, Jack." Rosie pressed a hand to her chest dramatically, giggling at Jack's laugh. She spun again, coming to an abrupt halt when she saw Simone in the doorway, the joviality falling from her face as she waved a hand awkwardly to the ecologist. "Hi."

"Hi, I'm Simone." Simone waved back with a smile, glancing at Jack questioningly. "When did Nikki get replaced by a teenager?"

Jack opened his mouth to answer, only for Rosie cut him off with a mischievous smirk. "I am Nikki, Simone." She directed wide eyes to Jack, who was silently trying to stare her down into telling the truth. "Nikki Alexander."

Jack shook his head with a smile. Nikki had been there with him to greet Rosie and get her things from Julia, which were currently being stored in Thomas' former office, but she'd had to rush off to a faculty meeting for half an hour, leaving Rosie in her desk chair as the teenager refused to go anywhere near her dad's former office. Not that either Jack or Nikki could blame her for that. They didn't really like going in there either, not with the knowledge of both Leo and Thomas being in there. "Don't start." He warned the fourteen year old, though his grin belied his stern words.

"Start what, Jack? I mean, come on, it's hardly my fault Simone doesn't remember that I'm Nikki." Rosie shot back with a grin.

"Jack?" Simone questioned in confusion, moving to sit at her own desk cautiously, still watching the pair.

"What? It's just me and Nikki, Simone." Jack gave in, unable to hold out for long against the pleading look Rosie was directing at him. He usually hid behind Nikki when the teenager pulled out that look, for Nikki had a far higher tolerance for that face than he did. "What's gotten into you today?"

Rosie giggled, settling back into Nikki's chair and doodling on the edge of one of Nikki's notebooks. She knew Nikki didn't care so long as she didn't draw over the actual notes. "Jack, are we still having pizza later?"

"Yeah, we are… Nikki. If you're not too annoying, anyway." Jack caught himself at the last moment, having been about to call her by her actual name. "So, how's the boyfriend?" Rosie had recently gotten herself a boyfriend from her class at school and though neither Jack nor Nikki could see it lasting, they'd kept quiet on that front and simply been supportive listeners for the teenager. She already had her mum and her mum's boyfriend telling her how unsuitable her boyfriend was. She didn't need it from them too.

Rosie shrugged. "Alright. I'm seeing him at the weekend. We text a lot."

Simone stared between the pair incredulously. "Did I step into a parallel universe or something?"

"Nope." Rosie grinned at her. "It's just another day at the office. What else would it be?"

"Strange if we had a call out." Jack rolled his eyes, replying quickly to an email. He glanced up, shaking his head lightly at Rosie. "You're a trouble maker, you know that?"

"Oh, I know." Rosie swung back and forth in the chair again. "I mean, I know who I am. I'm definitely Dr Nikki Alexander."

Jack bit his lip to stop the laugh that threatened to bubble up at Rosie trying to imitate Nikki's accent. "Of course you are, Nikki. Silly me."

"Nikki!"

Simone and Jack both jumped at Rosie's cry of the pathologist's name, looking up in time to see the teenager race through the office to where Nikki stood in the doorway, grinning. The blonde pathologist wrapped her arms round Rosie in greeting as the teenager snuggled into the hug. Her meeting had finished early, and she'd spent the last couple of minutes just watching Rosie pretend to be her in order to confuse the newest member of the team.

"You really are a trouble maker, Rosie." Nikki laughed out as she let Rosie go. "How much did you annoy Jack whilst I was gone?"

"Hardly at all." Rosie rolled her eyes goodnaturedly. "He threatened to withhold pizza if I was as annoying as last time."

"Jack." Nikki admonished lightly. "Just for that, you're paying for the pizza."

"What did I do?" Jack held his hands up in surrender as Nikki turned to Simone with a smile.

"Simone, this is Rosie, the daughter of a friend of ours." Nikki placed a gentle hand on Rosie's shoulder. "We get the pleasure of her company from time to time."

"Hi Rosie."

Jack glanced up, his eyes narrowed at Rosie. "Rosie, did you sign me up for spam emails?"

Rosie's grin lit up her entire face even as she hid behind Nikki for protection. "Well, you did threaten me with no pizza."

"Rosie!"