Castle had tripped a few blocks back and Beckett had only given him a quick glance as he'd tumbled to the pavement. She'd kept running, continued to chase the suspect through the city until he got away, the man turning unseen to her and leaving her standing at a junction, a little out of breath. She stood and wiped a hand over her sweaty forehead. She'd chased the suspect a long way, and needed to rest a little before making her way back to her car. And Castle.

She almost fell over him when she turned around to find him behind her, panting hard like a dog, tongue hanging out. He was doubled over, hands on his knees, sounding like he needed oxygen and fast.

"He got away?" he managed to get out, eventually, standing up straight.

"Yeah," she said, the word a puff of air. She was fitter than Castle, much, much fitter, but she wasn't invincible and they were chasing a former body builder. She needed some water.

Castle looked like hell, and she was aware she probably didn't look much better either, she'd just had the equivalent of a good workout. She could feel the sweat on her forehead, her neck, working it's way down her chest. She was glad she was wearing a black shirt.

"Damn, you look hot," Castle said, when he could breathe a little more.

"What?" she snapped.

He grinned at her. Just a few weeks ago, her tone and glare might've had him taking a step back, but now he just grinned. It was infuriating. Sexy, but infuriating. She had always liked it when men could stand up to her.

"The whole sweaty worked up thing, it's sexy," he said, moving closer.

"Castle say one more word-"

"Remember, my safe word is apples."

"I remember, and believe me, you're going to need it in a minute."

"You remember, really?" he said, the grin actually getting wider, something she didn't think possible.

She was about to reply, or hit him, she wasn't sure which, when a car pulled up beside them and Esposito leaned out of the window.

"You guys need a ride?" he said, almost laughing.

Beckett didn't reply, she walked around to the front passenger side, opening the door but pausing before she climbed in.

"You know, pit stains are not becoming Castle," she said, nodding towards his chest.

He looked down at the wet dark blue V around his neck, and the sweat rings beneath him arms. When he looked back up at her, she smiled, and he was wounded for a whole second before he replied.

"Did you just say becoming?"

She frowned.

"That is really sexy," he continued and with a growl, she got into the car.

z

"Hey Castle," Ryan said, snatching the leaflet the writer was holding, and dropping down into the desk chair next to him. "Gym membership?" He handed the leaflet to Esposito who was leaning against the desk, raising his arm in the arm so Castle couldn't snatch it back.

"Thinking about buffing up a little? Case got you feeling a little inadequate?"

"Beckett."

"We heard she left you collapsed on the pavement after just a few blocks yesterday," Ryan said.

"I didn't collapse, I just fell behind a little," Castle said, indignant at the mere suggestion. "I'm more of a sprinter."

"Is that so?" Esposito said, with a smile. "You don't need this place," he said, waving the gym leaflet at him. "Ryan and me'll help you out."

"Yeah, we can help you get cop fit."

"Cop fit?" he asked, raising an eyebrow.

"Yeah, cop fit, you know, eating a couple of doughnuts a day, fetching take-out."

"Lifting heavy boxes," Ryan put in. "All that cop stuff."

"We can have you chasing perps from here to Long Island in no time."

"Really?"

"Yeah, you can count on us bro."

"And I'll be able to keep up with Beckett?"

The two detectives shook their heads in unison.

"Dude, no one can keep up with Beckett," Ryan told him. "She's like a robot or something."

"Terminator," Esposito said.

z

Beckett opened the door to the stations gym, hearing harsh breathing from the machine room, and the odd unfamiliar grunt. She headed towards it, and saw Castle on one of the running machines in the otherwise empty room. She watched him for a minute as he ran at a decent pace, sweat dripping off his back, and smiled, impressed.

"Castle?"

He stopped running suddenly, and almost fell flat on his face as the treadmill kept moving and his feet didn't. He got his balance back on the solid, still, ground, and turned around to smile at her, blushing a little. He was hot, sweaty, his hair was standing up, and he looked entirely different to the last time she'd seen him like this. He looked good. He was wearing a vest, a well fitted vest, over the beginnings of a defined chest and she was definitely impressed.

"Hey, Beckett," he said.

"What are you doing here Castle?"

"Working out."

"I can see that. Why here?"

"Ryan and Esposito have been helping me out, you just missed them."

"I thought something had changed."

"You noticed?"

"Well, yeah, you usually last twenty blocks instead of just ten now," she said, smiling. "And your shirts are tight around your chest instead of around your stomach."

"Hey!" he cried. "My shirts were never tight around my-" he stopped, seeing her grin widen, realising she was making fun of him. Again.

"You're too easy Castle."

"I can be for you," he said, without missing a beat, that flirtatious grin that she hated, on his face a moment later. The flirtatious grin she used to hate. Now she just disliked it.

"Castle," she warned.

He simply grinned at her.

"Yes Beckett, would you like the machine?" he asked, innocently.

"No, thanks, I do enough running on the job," she said. "I'm gonna pound the bag."

"Can I watch?" he asked, eyes lighting up in a way that worried her.

"No."

"Can I stand by the door and listen?"

"Do you want me to use you as a punch bag Castle?"

"Would you think less of me if I said yes?"

She glared at him and took a few steps towards him, annoyed and delighted when he didn't back up, wasn't too intimidated. She stopped and turned to leave the room, pausing at the door and looking him over.

"You look good Castle," she said, he took a step towards her. "Come near this door and I won't give you the chance to use your safe word though."

He grinned at her and she left the room, not allowing her own smile out until she was sure the door was closed and Castle couldn't see her. No point in letting him think she was getting soft on him.

Even if she was.