So here's chapter 4. Enjoy :)

Once in the gym Beckett stripped off her shirt down to her tank top and dropped her gun and watch on top while Tony took off his jacket, shirt and gun. Ziva smiled and pulled her gun off her waist then bent down and unstrapped the holster from her ankle and then pulled the knife out of her belt. Seeing Castle's eyes on her she smiled at him and shrugged. Tony looked up and smiled at Ziva and then chuckled at Castle's face.

After putting all their stuff in a pile by the mats Beckett went and stood in the middle of them. Turning to Castle she said, "Come on Castle, you need to know the basics."

Castle huffed as he took off his jacket. Going to stand in front of Beckett he said, "I'll have you know detective that I do actually know some hand to hand."

"Oh?" Beckett said, striking out with her fist, just o test him.

He easily blocked it with his forearm and retaliated with a punch of his own, "Of course, writer remember. I like to know how to do what I'm having my characters do."

Beckett didn't answer just kicked his legs out from under him. He landed with a bang but quickly recovered and swiped Beckett's legs from under her too. She landed on top of him and he quickly flipped them, using his heavier body to pin her. Beckett relaxed for a minute then wrapped her leg around his and flipped them so she was straddling him and put her arm to his throat. After a few seconds spent breathing slightly heavier than normal Beckett stood and offered her hand to Castle, he took it and got to his feet. "Nice Castle, you've been holding out on us."

He shrugged, "I've got mad skills Beckett, you should know that by now."

She laughed and pushed him off the mat before turning to Tony, "Shall we," she questioned.

They spent ten minutes showing each other what they could do before Tony stepped back and turned to Ziva, "You're turn my little ninja."

She shook her head before walking past him and giving him a punch in the arm, "Get out of the way my little hairy butt."

Tony laughed and went to stand beside Castle and he whispered, "This should be good."

Tony was right. The two women had an unspoken agreement that they were going to go all out and not like what Beckett and Tony had done before. The two of them slowly circled each other then Ziva took the first step and swung her fist at Beckett, who blocked and kicked at Ziva's knee. She raised her leg and took the kick in the shin before stepping back and beginning to circle again.

The two went on like that for fifteen minutes, both going in and trying to land a hit but then stepping back after a few tries and continuing to circle. Ziva went in once more and kicked out Beckett grabbed her leg and overbalanced her. Ziva landed on her back on the floor but scissored her legs and brought Beckett down too.

The two of them lay panting on the floor and Beckett said, "Ok, time out. I think we've got the jist of each other's skills."

Ziva chuckled, "I'd say. You're good," she said standing and offering Beckett a hand, which she took, "I haven't had that much of a challenge in a long time."

Beckett smiled at her, "Thanks, but you would have had me if we went on any longer."

Ziva smiled and Tony came over, clapping, "I'm impressed, haven't seen any give Ziva a run for her money like that before."

"Thanks," Beckett said smiling, "I've had a lot of practice."

She walked over to where Castle saw holding her shirt and smiled, "Thanks Castle, but first I need a shower."

"Can I join you," he joked. Beckett glared at him and he said, "Or not."

Beckett shook her head and turned to Ziva, "I've got a change of clothes if you need them."

Ziva looked at her shirt and nodded, "If that's alright."

"Sure, come on." Beckett walked towards the changing rooms and lockers with Ziva following close behind. Once they reached the lockers Beckett quickly put her combination into the lock. Pulling open the door she threw the spare shirt she kept in there to Ziva and passed her one of the two tank tops, keeping the other one for herself.

She then went to the closet and pulled out two towels, passing one to Ziva and then walking past her to the shower.

Ten minutes later the two of them meet back at the lockers, each running a towel through their hair. Beckett pulled a comb out of her still unlocked locker and ran it through her hair before passing it to Ziva who smiled and quickly worked the knots out of her hair.

Throwing their towels into the laundry the two women walked back out to where Castle and Tony were talking about movies they'd liked. Beckett and Ziva glanced at each other and shook their heads, then snuck up behind their partners, "Boo," they both said at the same time and laughed as the two men jumped, Tony automatically going for the gun he had restrapped to his hip.

Castle glared at Beckett but then smiled at her and handed her the shirt he was still holding and her gun.

After Tony realised who was there he quickly relaxed and handed Ziva her guns and knife before saying, "You look nice Ziva, shirts suite you."

Castle and Beckett looked over and had to agree. Ziva was wearing the shirt open so you could see the tank underneath. Ziva studied Tony's face for a moment, to see if he was serious, then smiled and said, "Thanks Tony."

Beckett glanced at her father's watch, which she was in the process of strapping to her wrist, and asked, "Since you're agents I'm going to guess you can use a gun but I'm not sure we'll be able to conceal one if we're wearing leather," she paused for a moment then said, "Actually I know we won't be able to conceal them so there's no point in seeing how well you shoot."

Ziva and Tony nodded, but Castle asked, "Does that mean detective I'm finally going to see you straddling your bike in leather?"

"I don't know Castle, does it?" she teased.

He pouted. "Are you going to ride your bike?" he sounded like his normal nine year old on a sugar rush.

"No Castle, I was going to use a different one. Of course I'm using my bike and you're going to have to share with me."

Castle shook his head, "That's what you think."

Beckett wondered what the hell he was on about but before she could ask Tony asked, "You have a bike detective."

She turned to him, remembering that they were there, "Yeah, a 94 Harley softail."

"Now that is a sweet ride."

Beckett smiled, "Thanks." She turned back to Castle, "Explain your last comment please Castle."

He shook his head and then shouted, "Apples, apples," when she grabbed his ear and twisted. When she let go he said, "I have my own bike."

"Since when?" Beckett asked, not having heard this before.

"Since my first pay check," he replied smugly. Beckett raised her eyebrow and Castle hastily added, "It's a Suzuki GSF 250 Bandit."

Beckett nodded, "Looks like you're not riding with me then."

"I guess not." He smiled and she couldn't help the grin that spread across her face in response.

"So," Tony said, "Looks like we're the only ones who need bikes then."

Ziva shook her head, "Just you Tony."

"You cannot be telling me you have a bike in New York."

Ziva shook her head and Tony cocked his head to the side in question. Ziva sighed, "I've never ridden before," she said in a quiet voice.

Tony was silent for a few seconds as he processed what Ziva had just said then, with a big smile on his face, said, "Finally, something you can't do better than me."

Ziva punched him in the arm and as he rubbed it he said, "Well, Zee-vah, looks like you're riding with me."

"Great," Ziva said with an exasperated sigh.

Beckett smiled at the look on their faces and said, "Come on, we need to go get you a bike and leathers." She turned to Castle and asked, "I take it you have leathers?"

He nodded, "But I'm not sure if the trousers still fit so I'll wear jeans." He looked Tony up and down, "Although my spare jacket should fit DiNozzo so we won't have to sort that out for him, if he doesn't mind borrowing mine."

"That's no problem, thanks Castle."

Castle nodded and Beckett looked Ziva up and down and said, "The jeans you're wearing now should be fine and I have a spare jacket and a spare pair of boots if they'll fit."

Ziva nodded her thanks, "I appreciate it detective and I'm a seven."

Beckett smiled, "Looks like you're borrowing my boots then."

She looked at her watch again then began to walk back towards the stairs before Castle stopped her with a hand on her shoulder. She turned back to him and he raised his hand and pulled the chain of her necklace, bringing the ring out of where it had been stuck down her back and placing it back against her chest.

"Thanks Castle, I hadn't realised."

He shrugged, "I haven't seen you wearing it in a while."

She took the ring between her fingers before dropping it inside her tank top, "I only wear it when I need to feel close to her."

Castle nodded and Beckett looked over his shoulder and saw the questions in the gazes of Tony and Ziva. "It was my mother's ring. I wear it for the life that I lost and this," she pointed at her watch, "For the life that I saved."

Tony nodded while Ziva absentmindedly fiddled with her own Star of David necklace, "I know the feeling," she said, pulling it out and saying, "I wear this to remember my sister."

Beckett gave her a smile and the two of them walked away. Tony and Castle looked at each other and Tony commented in a quiet voice, "Those two a similar but different at the same time."

Castle nodded, "Yeah, I see what you mean. They're both strong, independent women but their personalities seem so different." He saw Tony give him a look that clearly said he couldn't have read Ziva enough to know her personality. "I'm a writer, I read people for fun and I've got good at it through years of people watching."

Tony just shook his head and the two of them walked back towards the bullpen.

I took a few liberties when it came to the characters but I do think that Beckett would hold her own against Ziva since she does train a lot and mostly with men.