"Mark," Addison attempted damage control, "it's not like that..."

"Dada!" Amy shrieked, reaching out to Derek.

Mark's face grew cold. "I think it is," he said scathingly, watching the little girl - his little girl - struggle to get to his ex-best-friend.

Mark had thought that when he came over to see Addison that Derek would be the one mad at him. He knew that Addison had come to Seattle, and he thought that it might to follow Derek. He fully expected for Derek to punch him in the face... And yet here he was, balling his hands into tight fists and trying not imagine how could it would feel to slam his fist into Derek's - was that smug? - jaw.

"How could you?" He rounded on Derek. "I know what I did was wrong, but raising my child? That's crossing a line!" He took a threatening step toward Derek, and Derek stepped back.

"Seriously, Mark," Addison implored, "calm down, please."

Now, Mark Sloan was not known for being a calm person, nor a fair, decent man. In fact, he was widely known to be a huge ass. And Mark decided to fulfil everyone's expectations of him - and when he finds out that his best friend has been raising his secret baby, who wouldn't? - and so he lifted his arm punched Derek square in the face.

Addison gasped and turned Amy's head toward her shoulder, but it didn't stop the strangled cry that came from her. Mark instantly felt a stab of guilt as he watched fat salty tears leak from his daughter's eyes, and slip down her cheeks.

Derek lay on the floor, blinking rapidly and clutching his jaw. "Jesus Mark," he breathed, the wind knocked out of him, "you've still got an arm on you."

"You - " Mark began incredulously, but he stopped. "You know what, I can't do this."

"No," Addison said desperately, shaking her head while trying to soothe Amy. "No, Mark..." He said nothing, just walked off.

Addison looked at the Chief, who was just watching the whole scene unfold with a bemused expression, and thrust the hiccuping baby at him. Then she took off after Mark.

"Stop!" She called out, rushing over quite skillfully in her heels.

"Why, Addison?" He snapped. "Why should I do anything you want me to. You know, I've spent the last two years feeling guilty over what I did to you, what I did to us. I thought that I was the bad guy, but you know what? I'm saint compared to you. You're just some stupid slut who took my baby and betrayed me with my best friend."

He wanted to stop there and leave with some dramatic exit, but he couldn't. He wanted to gauge her reaction, to see what she made of his monologue. He waited... And then she burst into tears.

Not one glistening tear trailing down one perfect cheek, but sobs that made her look so fragile that Mark felt irresponsible not to try and hold her together. Addison Adrienne Forbes Montgomery was always full of poise and perfection, never letting her confident facade slip... But this wasn't her, this was just Addie.

Addie who would stay up all night talking to him about things that never mattered, over things that she wouldn't give a second thought to except that she wanted to continue listening to his voice.

Addie who sang at the top of her voice without even realising, and then blushed the most adorable scarlet colour, like her hair, when she realised that he'd heard.

Addie who had spent three hours preparing a dinner that Derek had promised to be home for, having not seen anything other that the walls of the hospital for two weeks, and then had sat alone at the table, waiting for a husband that never came. But welcoming his best friend that did.

Addison Adrienne Forbes Montgomery could handle being shouted at. She could handle being called a slut and by being humilated in front in of her colleagues, and she could come back from that with more respect than ever. But Addie couldn't. She was sad and scared and raising a baby virtually on her own, and Mark loved her. And no matter what Addie did she was a woman that Mark could never hurt without feeling the bone crushing guilt after.

"Addie..." He said softly and he felt that it was entirely inadequate after what he'd said to her. "I'm sorry."

She sniffed and wiped the mascara tears off her cheeks. "I'm sorry," she repeated, looking so forlorn that it took all Mark's strength to not hold her and never let go right there. "You can say what you want to me, I deserve it. I get that I'm a horrible person, and I just thought that when you came back to me... I thought it would be easy. I didn't think about you or how you'd feel, and I didn't think about Derek. He's not with me, he has the intern... He's just there for me, sometimes. It's ironic that he's here for me now when we're divorced, and yet when we were together he was never here."

"He never saw you," Mark mumbled, thinking back to the night when the two of them had crossed that line and slept together. It hadn't felt dirty, or wrong... In fact, it felt more right that anyone else Mark had ever been with. Addie and Derek's bed was a bed he was used to, having spent many a night with his arms wrapped around a disappointed Addison, stroking her hair while she cried.

And that first night, he'd dared pretend that the beautiful woman currently in his arms was his, and that feeling had been better than anything else.

"You saw me," Addison interrupted his thoughts.

"I saw you," Mark agreed, then stepped forward and caught her lips in a passionate kiss. As they both fell back into familiar ground, each other's mouths a place they knew well, Mark let his tongue gently lower her bottom lip and slide in. The kiss was a perfect jumble of the past and the present and the future that could be, all rolled up into one complicated mess.

They broke apart a moment later, when air became a necessity. Addison gazed up at the man who she loved, the man who's child she carried and nursed...

"I saw you too," Addison whispered, stroking his cheek with her hand.

"I..." Mark started, but faltered. He did love her, he did, so much... But he couldn't bring himself to say it. "I think that you should take Amy," he nodded to the Chief, who was doing his best not to look at them.

Her disappointment was unmissable. She lifted her hand to wipe her tears, but Mark got there first. He leaned forward, and Addie thought he was going to kiss her again. But, instead, he wrapped his arms around her and pulled her flush against his broad chest. "Oh Addie..." He breathed. "We really screwed up didn't we?"

Her heart caught in her throat. We screwed up. He hadn't just said her, and she loved him even more for that. "We did," she agreed, chuckling softly into his shoulder. She was still a little tense in his embrace, but she soon just let go and let herself be engulfed. "Oh..." She breathed, tears pricking her eyes. It felt so good to back here.

"Addison," he coughed, not wanting to let go, "she needs you."

"Us," Addison corrected. "She needs us."

Mark let go, and instantly, Addison missed the warmth that his body provided for her. His hand still lingered on hers, gently intertwining their fingers.

God, he wanted so badly to be mad at her. So badly. But just looking at that face, those eyes... And he couldn't. He'd hurt her before, and all he wanted now was to make that better, and nothing she did would change that.

"Uh hem," Richard interrupted diplomatically, leaving Derek where he was. "Mama is needed," he elaborated, holding Amy out.

Addison smiled at her, trying to look happy. "Hi baby," she cooed. Then her pager went. "Shoot, I forgot that I came here for a reason," she frowned.

She turned to Mark. "Take her."

"What?" He asked. He wanted to spend time with Amy... But he was new to this. Fatherhood was not something he was practised at.

"Take her," Addison smiled encouragingly. "I'll be back in a few hours, and you two can...bond."

"Bond?" Mark raised an eyebrow.

"Mark," Addison held her out. "Go on sweetheart, go say hi."

Amy was placed in Mark's large arms, and then Addison looked on at them like the cat who got the cream. "Okay," she sighed, feeling drained from all the emotion. She kissed Amy's forehead. "Bye."

Mark watched Amy's little eyes follow her mother until she was out of sight. Then her little mouth opened and Mark could do nothing before she began to wail for her mama.

.

Mark bounced Amy on his hip, feeling less and less enthused with this as each minute crawled by. Jesus, how long could a kid take to be delivered?

It was close to two hours since Addison had left, and the only time Amy had not been crying had been to breathe in, to get more air to use for crying.

Mark hated to admit, but he felt like a failure. This kid may not know him, but that didn't mean that after two hours she wouldn't be calmed by him.

Switching sides, Mark realised how brave Addie had been. Sure, she was gifted with babies, but still... No matter how involved Derek was - and Mark begged that that was not very - he was still with the moderately attractive intern, who by the way couldn't hold a handle to Addison. And that meant that for all intents and purposes Addie had done this alone.

Well, he'd been at it for two hours. Two years alone... That was commendable.

Amy gave another wail, with renewed vigour. Mark sighed. "Alright, Amy, here's how it is," he said bluntly, not up to baby talk, "I'm not what you want, I know. You want your mommy, and at this moment, so do I. But right now, I'm all you've got."

She wailed once more, and Mark was this close to giving in and finding Derek. Little did he know that Derek had already found him.

"She likes it if you rub her lower back," Derek mumbled from the doorway, looking superior as ever. "And she loves it if you sing, but only Addison does that."

"I can handle this," he said through gritted teeth.

"Just try it," Derek pushed. "All this crying's not good for her."

"Are you saying that I can't look after my own kid?" Mark snapped, but at a low tone so as not to alarm Amy.

"Are you saying that you can?" Derek challenged, and so help him God if he hadn't been holding a child Derek would have been back on the floor before he knew what hit him. The blooming bruise was giving Mark a sense of satisfaction though.

"She's mine," Mark told him firmly. "Not yours. Mine." Who cares if Derek knew how to get her to stop crying? He could learn - he would learn - and he was the dad. He called the shots now.

"I know," Derek nodded. "I've never tried to be in your place."

Mark snorted. "She calls you daddy!"

"She doesn't know what she's saying," Derek scoffed. "And if you're back for good, I'm not going to get in your way."

"Really?" Mark said, with a mock impressed expression. "Can I just ask, Derek, what was going through your mind when you got involved with this? You know, after you two divorced and all."

Derek was silent for a moment, contemplating. "Just a welcome little window into the life I could of had," he said finally, and Mark was humbled by his answer.

"Look Mark," Derek continued, "Addie may have cheated, but I was the one who gave it all up. As soon as I started something serious with Meredith, that was it. And I love Meredith, I do... But I loved Addie. For over a quarter of my life. And no matter what happens, that counts for something. And seeing her in mommy mode," Derek's eyes crinkled, "just makes me see what an amazing mother she makes, and would have made to our kids."

"And she makes to our kid," Mark couldn't resist adding, looking at Amy. It was then he realised that while they'd been talking the crying had stopped. Amy was fast asleep, in his arms.

"She loves you," Derek told him.

Mark looked up. "She's barely known me a day," he pointed out.

Derek smiled faintly. "I wasn't talking about Amy," he said, then left.

Sitting in the dark, despite himself, Mark started to smile.