A/N - Happy Holidays! I'm sorry, I know I said I'd update this story a lot faster but I got really busy with finals and then Christmas. I'm on break now, so I should be updating a lot more frequently. Hopefully once a week even when school start's back up. Let me know what you think!

Also, I really went away from the show in this chapter because I wasn't really sure how to write a fight scene. This lets me use my imagination a little more, so hopefully it will be a lot easier to write like this from now on. I won't go too far away from the plot of Grey's, and I will probably still keep some scenes the same. Also, hopefully these author's notes will be a lot shorter in the future. Let me know what you all think!

Lexie thought about chasing after him, but she didn't want to make a scene in front of the whole hospital. She thought to herself, what if he really liked her? What would happen then? Would they tell people? Obviously almost everyone would resent the idea of them together. Especially Meredith… and Derek… Could they keep it a secret? Would a relationship between them even be worth it?

Lexie snapped out of her thoughts quickly and left the supply closet and went to one of the on call rooms because didn't want to be as far away as Meredith's house when she was on call. She walked into the dark room and shut the door behind her. She took her scrubs off and changed into a more comfortable tee-shirt and some shorts.

"I'm trying to sleep you know." A deep voice grumbled from the other side of the room.

"Oh, I-I'm so s-so sorry, I'll," she said as she turned around. "Wait. Mark?"

"You got me," He replied.

"Are you on call?"

"No. My apartment is getting redone and I don't feel like having Callie lecture me."

"Oh, um, okay," Lexie said awkwardly as she slipped into a small bed on the other side of the room. She lied there with her eyes open, unable to sleep. Mark, on the other side of the room, turned to face her. Lexie could feel his eyes on her body. After a few minutes of silence she spoke.

"What are we?"

"What?" He replied.

"You know what I said."

"I don't know, okay?" He replied "You're Meredith's little sister. You're forbidden, and I promised Derek I'd stay away from you."

"Well how's that been working out for you?" Lexie asked with a chuckle. Mark smiled and got out of his bed to join her.

"Come here." They both laughed as he rolled over and pulled her on top of him. She leaned down and gave him a short kiss on the lips. She moved to his cheek, down to his neck, then to his chest, and then further.

Meanwhile, outside the doors to the, now, locked on-call room.

"Oh no, not again!" Called out one of the interns.

"Yep."

"But I need sleep!"

"Woah woah woah, hey, you guys need to leave. There's other on-call rooms, go sleep there," Callie said as she walked up and heard the laughter of her best friend. The interns walked away, and Callie knocked on the door. Suddenly the room fell silent. "Mark it's Callie, I know you're in there. Open up!" She yelled through the door. She heard a bit of stumbling around until the door finally unlocked. Before Mark got a chance to say anything, Callie had already barged through the door. "You guys need to be more careful. I just found three interns standing outside listening to you guys. They needed the room." Mark turned to Lexie and they made nervous eye contact. "Well, anyways, Mark, I need you for a consult. Meet me in trauma 2." Callie walked out and shut the door behind her.

"Mark, if we're going to have a relationship, I need to be in it in front of my sister, and in front of Derek. I don't want to hide."

"I'll tell him," he said as he put his scrubs back on. Lexie sat up and looked at him.

"Until then, we can't do this."

"Yeah, I know. I'll tell him. Soon…" Mark left the room.

"Lexie, what's up? You look sad," Sadie said as she walked up to Lexie at a nurse's station.

"Oh, um n-nothing."

"Uh oh, no no no I know that voice." Sadie looked around until she spotted Mark, right in Lexie's line of sight. "Stop staring, he'll tell Derek when he's ready."

"Sadie, it's been a-a week. He probably isn't telling Derek because I'm not worth it."

"Oh please, Lex. What has he been doing this whole week? Every time he talks to you he starts flirting."

"Ugh," Lexie replied as she turned back to look at Mark.

"Grey, Sloan asked for you," Cristina barked in the locker room.

"Why is she always with Sloan?" One of the interns asked, failing to whisper. Lexie rolled her eyes and walked away, nervous to see what Mark had to say today.

"Hey, um, you asked for me?" She said when she found mark by the O.R. board.

"Yes," he said without turning away from the board. "I need you to diagnose something."

"Um-okay? What are your symptoms?"

Mark looked at her and smiled. "Well right now I'm battling a rapid heart rate. I'm also feeling a little flushed, and I don't even want to mention what's going on the belt."

"Hey! No, no, no, I'm not doing dirty secret flirting with you until you talk to Derek. Now give me your patient's symptoms."Mark laughed and proceeded to show Lexie his patient's scans.

After the surgery, Lexie and Mark walked down the hallway back to their patient's room together. Little did Lexie know, Mark had a different agenda. As they walked, Mark discreetly looked around and over his shoulder. At the perfect moment, when no one was looking, Mark grabbed Lexie and dragged her into a supply closet with him.

"Oof, wha?-" Lexie said as she stumbled into the room. Mark shut the door behind him and stood in front of it so Lexie couldn't leave. "Mark, what are you doing?"

"Ok, I know you said we can't be together until I tell Derek. I promise I'll tell him but I can't wait to be with you." And just like that he had already pushed his lips against hers in a deep passionate kiss. Unable to resist, Lexie sat up on the table and pulled his shirt off. Mark lied her down and climbed on top of her, throwing her shirt to the ground without breaking the kiss. She ran her hands along his abs as he untied her scrub pants.

"Yes, Mrs. Littleton, I'll get you some towels too." Derek said as he left his patient's room, heading towards the supply closet.

"Hey! What's up?" Meredith said energetically as she caught up to Derek in the hallway.

"Wow, someone's happy," he said as he continued walking "I'm just getting towels for my patient."

"Oh nice! And yes, I'm happy because I just saved a man's life."Derek chuckled a little. Meredith continued, "Does your patient need those towels right away?" She asked, a sly smile on her face.

"I guess not… why?" He said, realizing what she meant.

"Quickie in the supply closet?"

"Oh, you don't have to ask me twice. Come on."

Meredith and Derek hurried down the hall, picking up the pace. Unsuspecting, they got to the door. Derek opened it without looking in.

"After you," he said, gesturing into the room.

Lexie and Mark were startled by the door opening and they hurried to cover themselves. Laughing, Meredith walked in. She stopped, in shock of what was right in front of her.

"What's wro-" Derek started when he walked in and saw his best friend, Mark, and his girlfriend's little sister, Lexie, lying there, barely covered. There was a moment of silence until Mark started.

"Look, before you say anything-"

"Oh my god," Derek interrupted Mark and walked out.

"Meredith?" Lexie reached out.

Meredith's eyes widened and she raised her eyebrows slightly. She shook her head, dropped her head, and walked out. After she left, there was another awkward silence.

"Well, now Derek knows," Mark said, only half jokingly.

"Mark! That is not how they were supposed to find out!"

"Lexie, does it matter how they found out? They'd know eventually."

"Mark, sh-she's my sister, and we just started to get to know each other. N-Now, I've probably ruined that and she'll never talk to me again."

"Lexie," he said, putting his hands on her face, "calm down. It'll be fine. They just need to cool down. Now, we can prove to them and to ourselves that we can be a couple."

"But Ma-"

"Shhh," he put his finger on her lips. "Let's show them what we can become. We can adapt to a hostile environment."

"Okay, lets go," she said. She kissed him once more and then proceeded to put her scrubs back on.

"Lex, come to my place tonight."

"Okay," she said with a smile as she left the closet.

A/N - Sorry for that ending. Idk, I wasn't really sure. Anyways, let me know what you think! Hopefully the next chapter will be out either tomorrow or the next day!