In case you need reminding, chapter 9 ended on a little bit of a cliff hanger. Derek and Mark were fighting, Derek stole Mark's car, and then ditched the party (and more importantly Addison) to help a very special patient. A patient that seems to mean more to Derek than any patient he's ever had. I mean, how often does Derek Shepherd cry over a patient? Maybe there's more about this patient to be discovered?

Anyways, Derek walked in on Mark having sex with someone. Read on to find out who this someone is.

…

"Dude get the fuck out," Mark yelled.

Derek frantically started stumbling backwards out of the room.

"DUDE OUT!"

Derek felt a sharp pain in his arm and realized that he had bumped into the door casing. He continued fumbling backwards and finally found himself in the hallway. Before the door closed, the last thing he saw was a very naked Mark slamming it shut.

What the fuck?

He stood frozen in the hallway staring at the closed door.

"Derek," a voice called from behind him, "what's going on?"

Derek turned around and looked at her, still unable to speak.

"Honey, what's wrong?"

"Mark and..." Derek trailed off.

"Mark and who," she asked. "Derek you're scaring me."

She pushed past him and started walking towards the door.

Derek took hold of her arm and said "no!"

"Derek what the hell?"

He took a deep breath and said, "Mark and Savvy."

"What about Mark and Savvy," Addison asked.

Derek responded by taking her arm and walking her down the stairs. When they reached the bottom she snatched her arm from him defiantly and put her hand on her hip.

"Let's go outside," Derek said.

"I am not going anywhere with you."

Derek took a patient breath but before he could say anything Addison continued.

"You left" she yelled, "and then you come stumbling home in the middle of the night trying to drag me outside, so we can talk?"

"Addison-"

"No, Derek," and she turned to go back towards the stairs.

"Mark and Savvy are having sex," he finally said.

Addison froze.

"Yeah, so I wouldn't go up there if I were you."

"Are you serious," she asked.

Derek nodded.

"Savvy," Addison questioned, "and Mark?"

Derek nodded again and said, "now can we go outside?"

She stood for a moment contemplating his question. Derek had no doubt she was trying to push away her shock and focus on the anger she felt for him. He knew if they stood too much longer she would find it.

"Addison, please," he begged, reaching for her hand.

She bypassed his hand and walked towards the kitchen on her own. Typical Addison.

"Are you coming," she hissed, without turning around.

Derek sighed. It seemed as if she had already remembered how to be angry, but at least she was willing to talk.

"Well," she asked when they walked out onto the back patio.

He glanced over at her. She was standing across from him in typical battle position. She had defiantly crossed her arms as if to lock herself away from him. This was yet again, a typical Addison move.

"Silence, just as I expected," she said with a fake laugh and pushed her hair back. When she did, she stumbled back a little but recovered quickly by leaning on the wooden beam.

Derek fought back a smile. She was clearly several drinks beyond drunk or she wouldn't have stumbled. Say what you want about his wife, but she knew how to hold her liquor. So for her to stumble, she was quite drunk.

"Derek if you aren't going to say anything, I'm going to bed."

"Addie," he finally said. "I'm sorry."

"Wow," she laughed. "That's all you have to say?"

She walked around him and towards the door. "Enjoy sleeping on the couch."

"My patient died," he said. "The patient I've had for months that I was close to. He died. I know it isn't an excuse, but he's gone. I couldn't just not go. He had no family, no friends, and he-"

Addison paused in front of the door when she heard his voice break. Derek frequently became invested in his patients, but this seemed to be more on an emotional level than before. She stood with her back to him, desperately wanting to stay mad, but finding it hard.

"He was an incredible guy, and he died all alone. I know that isn't your fault, but I couldn't just leave him there, Addison. I couldn't do it."

Addison took a deep breath and fought back her own tears. She herself was not one for waterworks, but Derek crying always had a way of breaking her. Thankfully he didn't do it often, but when he did, it absolutely destroyed her.

She turned around and finally looked at him. "I'm sorry," she said, sincerely.

"No one should be apologizing but me," he said. "I'm sure you had a terrible night."

"Actually, it wasn't bad," she confessed.

He raised his eyebrows at her.

"Okay," she admitted, "I was furious, but I found solace in the fact that everyone else was too."

"Dear god," Derek mumbled. "I don't even want to imagine the things that were said."

"Maybe you should. They were quite funny. Everyone joined in."

"Even my mom," he asked.

"Much to everyone's surprise, yes. Carolyn called you a workaholic and admitted that you have been neglecting our marriage."

"She's right," he said. "Addison, I really am sorry."

"You're always sorry, Derek. But then nothing changes."

"It will this time," he said sincerely. "You just have to give me a chance to prove it. While I was at the hospital I went ahead and assigned residents to my night and weekend shifts."

"Derek-"

"And I put in one week for Thanksgiving and two weeks for Christmas."

Addison walked over to the patio table and picked up a glass that Derek had not noticed. She took a sip of what appeared to be a vodka tonic with very little tonic.

"Addie, if you just give me a chance to fix things I will."

She took another sip and tried to focus on its contents rather than looking at Derek. Based on his voice she could already tell what his face would look like. And based on her experience with that face she knew it would be even more difficult to stay angry at him if she looked.

"Addie," he mumbled from right behind her.

She jumped realizing how close he was and then felt his hands on the sides of her arms.

"Can you please say something," he asked, and began rubbing small circles on her arms.

"I don't know what you want me to say Derek."

He moved his hands to her waist and said, "that you'll give me a chance to show you I can be better."

Addison took a deep breath but quickly realized it was a mistake because all she breathed in was his cologne.

"I know there's nothing I can say to fix this right now," he assured her. "Time is the only thing that will prove it, and I promise if you give me time I will make it up to you."

"I don't want you to make it up to me. I want you to change."

"I understand that."

She turned around and looked at him so that she could raise her eyebrows.

He knew what that meant so he responded immediately. "Yes, I do actually understand."

He watched her pursed lips part slowly and her arms uncross.

"I'll forgive you with one condition," she said, with a tone that sounded only half serious.

He gave her a smile and responded, "absolutely anything."

"You now have to get just as drunk as me."

Derek couldn't help but smile. Addison never admitted she was drunk to anyone except for him. She could be ten drinks in and if there was anyone other than Derek around, she would walk a straight line, while insisting that she was "only a little buzzed." This was one of their many little inside moments that they had not ever discussed, but they both knew it. Derek was the only one ever allowed to know that she was drunk.

"Hmmm," he said, pretending to contemplate her condition. "Do you get to pick my poison then?"

"Vodka," she answered. "You have some catching up to do and that will do the trick."

...

"Mark and Savvy had sex."

"Please stop saying that, Addison."

"I can't help it."

Derek shook his head and said, "I want to forget."

"You saw both of them…" Addison trailed off.

"Completely naked," Derek finished.

"And how was that," Addison asked with a laugh.

Derek answered by taking another swig of his third drink.

"At least you aren't Weiss," Addison mumbled.

Derek took yet another big gulp of his drink.

"I mean, I thought they were perfect. They're Savvy and Weiss," she said.

Derek sat quietly and let her ramble while he finished his drink. She ran through the story of how Savvy and Weiss met, as if he wasn't there for it, but he let her talk without interrupting.

When she finally finished he stood up quietly and said, "another," and lifted his glass to ask her if she also wanted more.

She handed him her glass and held up one of her hands so that he could help her out of the chair.

"I mean, they've been together as long as us, Derek."

"I know," he mumbled, as he led them both back inside to the kitchen.

"This is just completely out of left field, right?"

Derek said nothing and poured their drinks.

"Derek," she questioned. "This is completely out of left field, isn't it?"

"Let's go back outside."

"Oh, no-"

Before she could finish, he took her hand and led her back through the door and onto the patio.

"Well, start talking," Addison insisted as soon as the door closed behind them.

"Weiss called me."

"Derek is that supposed to mean something or?"

"He asked me to invite Savvy to the beach because things have been... difficult for them."

"Difficult how?"

Derek sighed and said, "I don't know Addison."

"What do you mean you don't know?"

"Why do you always need every single detail," he asked.

"Why do you always need to leave out every single detail," she countered.

"Okay, fine," he surrendered. "Weiss didn't say much, but he mentioned working more and that it upset her."

Addison let out a loud cackle.

"What's so funny," he asked.

"Oh, nothing. Just seems like we really are all going through the same shit."

"No," Derek quickly responded.

Addison glanced at him suspiciously and tilted her head. "What do you mean no?"

"I just got a different feeling from him," Derek said.

"Derek Christopher Shepherd if you do not stop with this vague storytelling."

Derek walked over to the edge of the patio and stared at the beach. Even though his back was to Addison, he could sense her frustration. Her foot was tapping quickly behind him and he could hear her huffing.

"Weiss asked me to see if Savvy wanted to get away for the weekend, but he asked me not to say anything to you or Savvy about it being his idea."

"Derek, I don't understand how that is-"

Derek cut her off and said, "Addison, I think he's having an affair."

They stood silently for a moment with nothing but the sound of the waves crashing in the background. Addison digested his words and what they meant. Derek would not ever accuse someone of that unless he knew, especially one of their friends.

Addison said, "I can't believe you didn't tell me."

"I did try," Derek insisted.

"Is that why you kept asking if Savvy was acting weird," Addison asked.

Derek nodded and turned to face her. "It's also why I got so upset when you said Weiss is a better husband than me."

"I didn't mean-"

"I know," Derek said, "I just wish I would have told you the truth as soon as he called me."

"To be fair, we were dealing with our own issues."

Derek nodded in agreement and said, "to say the least."

Addison sat down in her chair and propped both of her elbows on her knees so that she could put her face in her hands.

"What is it," Derek asking, sensing her frustration.

She responded by mumbled something inaudible into her hands, but Derek didn't even have to hear her to know what she was saying.

"Addie, you're an amazing friend. Just because you didn't guess Weiss was having an affair-"

"How could I not sense something," she asked cutting him off.

Derek walked over knelt down in front of her so that he could take both of her hands.

"Because you are a positive person that also happens to be a hopeless romantic. You assumed Savvy and Weiss were happy."

She stared at their hands for a moment and then looked up at him. "Derek, if you ever cheat on me I swear..."

"I will not ever cheat on you."

"Good because I will kill you and make it look like an accident."

Derek smiled at her and said, "even though I'm positive you could actually pull that off, I promise you won't ever have to."

She leaned in and kissed him quickly.

Derek gave her one of his signature soft smiles and then stood up. He reached for her hands and pulled her up out of the chair. When she was standing, he quickly sat down where she was and reached back out for her and said, "come here."

She sat down in his lap and angled herself between his arm and chest so that he could wrap his arms around her waist.

As soon as they got comfortable he mumbled "shit, we left our drinks on the counter inside."

Addison pushed herself up and headed towards the door to get their drinks.

When she walked back out with them Derek was standing up and he pointed towards the beach. "Let's walk down to the water."

She gave him a big smile and nodded. They had not done that in forever, and they both needed it. After all, they had purchased the beach house because they both agreed that the tranquility of waves would be the perfect addition to their lives.

As if reading her mind Derek asked, "when was the last time we actually walked down to the beach?"

"Too long. Especially considering that we spent a fortune to be this close to it."

He responded by reaching down and linking his fingers through hers. He could feel the condensation on her palm from bringing his drink to him earlier, but he ignored it. He squeezed her sweaty hand and said, "it was a good purchase."

She nodded in agreeance and said, "less than fifty steps from the patio."

"God, the amount of times the realtor said that."

She laughed and said, "he knew how to sell it."

"But have we ever actually counted," he asked.

"Do we actually care?"

Derek shook his head and plopped down in the sand. He reached for Addison and wrapped his arm around her waist when she sat down. She leaned against him and pulled her legs up to lay them on his. They both rested their heads against each other and sat listening to the waves that were only fifty small steps from their much too expensive beach house.

...

"Addison," he mumbled, breaking the silence.

They had been sitting silently for several minutes enjoying each other's company and the sound of water crashing against the sand.

"I thought it was you," Derek continued.

"What," she asked.

"When I walked in on Mark and Savvy, there was a brief moment where I thought it was you."

Addison turned to face him and said, "you thought that I Addison Montgomery-Shepherd was having... sex… with Mark Sloan?"

"I know it sounds ridiculousbut-"

"Derek, it's more than ridiculous. It's-"

"Disgusting," he asked, with a hint of hopefulness in his voice.

"Derek, I would not ever sleep with someone else. Especially Mark, and not just because he's your friend. Mark is just so…"

Derek nodded, completely understanding what she meant. He loved Mark like a brother, but he was just very…. Mark.

"You know, I thought you liked him," Derek confessed.

Addison made a disgusted face and said, "when?"

"When we first met," Derek answered. "I thought you were staring at Mark because all girls stare at Mark."

"Derek, can I tell you something that I've never told anyone?"

He leaned his head in to give her a look that obviously answered her question but he said, "you know you can tell me anything, Addie."

"On the very first day of med school, I was studying before class-"

"Of course you were," Derek interrupted and gave her a soft smile.

She rolled her eyes and continued, "so I was sitting at the coffee shop, you know the one across from the Harkness building?"

Derek stared for a second and she could see him mentally walking back through campus. "Wait, yes," he said, finally making his way there.

"Well, I was in there studying and Mark sat down at my table and started flirting with me."

Derek rolled his eyes and said, "of course he was. What an ass."

Addison gave a halfhearted laugh and said, "I was very uninterested in case you were wondering. I left him at the table alone."

"I can't believe he never even mentioned that to me."

"I can't believe I've never mentioned it to you," Addison confessed, "I guess it just seemed weird to say when we first started dating, and then I forgot."

Derek pulled her closer against him and kissed the side of her head before saying, "I'm not mad, Addison."

She turned her face into his neck and kissed him back, "I know."

He wrapped his arms tightly around her, and they sat silently for several more minutes before agreeing that they should walk back to the house. When they walked in, they made sure to keep quiet, in the hopes that they would not wake Mark or Savvy.

When they were finally laying in the darkness, Addison broke the silence and said, "Mark and Savvy had sex."

"Stop," Derek said.

"And you saw them both naked."

"Addison, I am begging you to stop."

"You saw Mark and Savvy having drunken adulterous sex in our guest bedroom at your sister's birthday party."

"Wait," Derek said, suddenly remembered the empty house. "Where did everyone go?"

"Your mom decided to stay at a hotel because our house is too cold, and she invited the girls for a sleepover."

"Ahhhh, better than her being here and complaining."

"Whatever," Addison said, "I'm not upset, but I am exhausted."

"I am too. Maybe we should sleep."

Derek sat up and gave her a quick kiss. "Good night."

"Good night," she mumbled in a sleepy voice. "I love you."

"I love you too."

…

Shout out to the few people that guessed that Mark was really sleeping with Savvy. I was hoping someone would!

For those of you that have read my other fic The First Day, I hope you noticed/enjoyed the little references to that. If you haven't read, then this is me shamelessly promoting it.

Anyways, that was chapter 10. As always, if you enjoyed, please leave a review. xxx