He hadn't thought of her in a very long time, until that moment - eight years to be exact. That's how long it had been since she died. That's how long it had been since the brother of the woman he was in love with had shot her in the head, at point Blanc range.

He never cried at her funeral - well, not much - not because he didn't care for her - he did - he almost loved her - like a sister - but he felt like he was letting her down if he cried; like he was not doing his job.

He thought back to the time he had Y. Pestis. They had talked for a while, about how they'd always have each others back. How they would take a bullet for each other… how they'd always be a team.

His thoughts were interrupted by a short Israeli entering the squad room.

"Good morning, Tony. You stayed late."

"Yeah, I had... uh… lots of work to do."

"Of course you did…"

"What's that supposed to mean?"

"Nothing, nothing…."

"God, you're starting to sound just like Kate!"

Ziva stood up sharply, and left the squad room.

"Well done Tony."

"Shut it, McNosyPosy!"

He stood up and headed in the direction Ziva went, finding her on the floor next to the vending machine. Ever since her father died, she showed her more vulnerable side, rather than her bad-ass one.

"I'm sorry, Ziva."

"Uh huh…"

"I am, I really am. It's just… it's a tough week."

"Want to share?"

He pulled a picture of Kate out of his wallet.

"She… She would have been forty this week. She always said that she wanted to have kids and be married by the time she was forty. I remember, once, I had Y. Pestis, and she had to be incubated with me in this little glass room for several days. We talked about future plans, vacations… and then I got really sick… it almost killed me."

"I'm glad it didn't." She smiled, and took his hand in hers. She gripped his fingers gently as he continued to speak.

"Anyway, I talked about my ideal woman… and I had no idea that only a month later, I would meet her."

"What did you do?"

"I got told to follow her, so I did. We ate Pizza and drank Coffee outside of her hotel."

"That's nice."

"It should be. Do you remember?"

"Of course I do… now do you want to tell me what you were really doing in the squad room?"

"I was writing a letter…"

"To whom?"

"Kate…"

"But she's dead. She's never going to read it."

"I know, but it makes me feel better."

"About losing her?"

"No… about letting her down. I've come to terms with the fact that she died. I haven't accepted the fact that I let her down. I did everything I said I wouldn't do. And I didn't do the things I said I would."

"Why do you think you let her down?"

"I didn't protect her and I said I would. Then she died. I was there. I was standing on that rooftop, and I didn't do anything to save her. I had this gut feeling, the one that Gibbs had, that something was wrong the minute we stepped onto that rooftop. The minute we stood there, when she started talking, I could feel it - the intense fear; the tension…. I could feel it happening around me - I could feel the atmosphere get darker - like happiness just drained from the world. And then her shot her… he just did it. She fell back, and blood sprayed everywhere. I let her down."

A tear rolled down her cheek as she gripped his hand tighter.

"I'm sure she knows that you didn't let her down. You never did. You didn't know that my brother was going to shoot her; you never could have known it if you tried."

"Did you know?"

"Excuse me?"

"Did you know he was going to kill her?"

"No. I knew my brother was here, but I didn't know his plans. I was never involved in that aspect. I called him once or twice, but he was never allowed to reveal anything to me. I was there to protect him if he got into trouble, but I never knew he was taking part in murder. If I knew, I promise you, I would have done anything and everything in my power to stop it."

"Why would you? You had to kill your brother."

"I may be an assassin, Tony… But I'm not a murderer. I only follow orders."

"Do you regret it… killing your brother?"

"No… I miss him dearly, but I do not regret it. I wouldn't be the same person I am today. He would have continued to hurt more people, and I would have found out, and I wouldn't have been okay with that. Its safer now that he's not here, and I miss having him around… someone who I can call in need; someone who I could tell anything to…. But no I don't regret it."

"You're a strong woman, Miss Ziva David."

He kissed her hand, and let go of it gently, standing up, and reaching out his own hand for her to hold. She smiled, and gripped in gently, walking back into the Squad Room with him, their hands falling apart the minute they heard the elevator 'ding'.

To their surprise, it was only Doctor Mallard who walked out.

"Good evening, Ziva, Tony, Timothy. Will you all be joining Gibbs, Abby and I for dinner?"

"Of course we will, Ducky."

They all grabbed their coats and headed to their cars.

"Do you want to take my car?" McGee said as they approached the parking lot, "Theres no point in taking all three."

"Sure." Said Ziva, smiling. "Tony, are you coming?"

"Yeah, yeah… I'll meet you guys there… Theres something I need to do first."

Ziva, McGee and Ducky all got in the car, Tony getting in his own, before pulling out a letter from his pocket. As the others drove away, he sat in the car, thinking about the times Kate and himself had shared… the time they were undercover in the pregnancy clinic; all the sarcastic comments they shared; the fun times… and the worst of them.

He got out of the car, and knelt down by the side of a stone plaque.

He took the letter out of his pocket, opening it.

He decided to read it aloud.

"Dear Kate,

I wrote this letter a while ago… well this morning actually, and I thought you should hear what I wrote.

Happy Birthday. Today, you're forty. Yes, the big 4-0. I'm sorry I haven't been here in a while, but I haven't had the courage. The last time I saw you, they were putting your body into the ground in a coffin, and I couldn't bear the thought of it. I couldn't bear the thought of not having my partner around. You were like the younger sister I always wanted. We constantly teased each other, and got on each others nerves, but we still cared about each other through it all.

Your sister came by a couple of years ago; I just thought you should know. She's a lovely woman. She seems to remember everything about me - the things you told her. I was quite surprised. It was a tough subject, talking to her about you. I hadn't really mentioned you in years, and it all felt like some hazy dream. I'm sorry I didn't mention you sooner… I just felt like I was betraying you, and being selfish if I allowed my mind to ponder over our memories… the good and the bad. I'm also sorry that one of our final memories was me opening that damn letter, and releasing probably the most deadly airborne virus on the planet.

I have a new partner now, alongside McGee… I just thought I'd mention it. She's incredible. She's so beautiful, and kind, and smart, and she's a total bad-ass I know you'd approve of her - she constantly tells me off for doing something or other… you and her would have been great friends. She killed her own brother to save Gibbs, if it's any consolation. Oh, her brother was only half related to her….. Ari. She killed him in Gibbs' basement. She saved him. I can't imagine how hard it must have been for her to do that. I knew it was hard losing you, but losing someone who you have been close to for years, throughout your childhood is the hardest part. I know, believe me, I know.

Anyway, I'm in love with her. Her name's Ziva. Ziva David. She belonged to Mossad, until we managed to steal her away from them. She's now an NCIS agent - Israeli though - and she's very good at what she does. Did you know she used to be 'Officer David?' I thought that was kind of cool. We're very close, I have to admit, and we're almost at the point of breaking rule #12…. Almost. I want to, and I think she wants to, too, but I'm not sure. I wish you were here right now to offer advice.

I have to admit that I cried while writing this letter… especially at this bit…. As it gets kind of deeper. (Yes, I know… deeper - Ziva changed me, okay?)

I have to apologise. I said I had your back that day. I said I always had your back, but you died, and it was my fault. You shouldn't have done. I shouldn't have let it happen. It was all my fault. We focused so hard on trying to save Gibbs that we forgot what was also important - each other. I promised you that I would look out for you, and I broke that promise. That day on the rooftop, I felt the air get darker; the atmosphere changed, but I restrained myself from saying something because I didn't think that it mattered. I didn't think it would be important. I didn't trust my instincts. But I should have done. I knew something bad was going to happen - I had a gut feeling, and both you and Gibbs told me a long time ago to trust my instincts but I didn't. I thought about telling you. I thought about telling Gibbs. I thought about getting ourselves off that rooftop, and down to a level which was safe - inside, where we could make sure that we could get him before we took a risk. I'm sorry. I didn't do the things I said I would, and I did all the things I said I wouldn't. I understand, if you don't forgive me - I wouldn't expect you to.

I still cry about you, sometimes… I even named my goldfish after you because I was in such despair. I remember the time you told me that you'd put GPS trackers on your kids, and never let them out of your sight. I remember the time that you said you'd thought you'd die, before what I assume was me admitting that you were right. And then it happened. You go shot, and we saw it. Your blood splattered everywhere… and you just fell to the ground, silently, and so still. You didn't move, and I thought that maybe, just maybe, if I had done something, I could have saved you. I could have saved your life… but I didn't. I'm sorry you never got to have the life you had planned - the life you wanted. I'm sorry you never got to have children and watch them grow up. I'm sorry you never got to tease me about being a father. I'm sorry you never got to see the man I became after that day…"

Tears were rolling down his cheek, as he put the letter in his pocket. His hand reached out, and stroked the stone, his fingers running over the engravings:

'Caitlin Elizabeth Todd: May 22nd 1973 - May 25th 2005. A beloved friend, sister and daughter.'

His voice went quiet, as he spoke

"I'm so sorry, Kate." He laid a bouquet of flowers onto the stone. "I failed you."

He stood up and walked away slowly. He could have sworn that he heard her faintly say:

"You didn't fail me, Tony… You never did."