She knocks on the door of his apartment - oh how she loves that door - hoping to see him there behind it. Instead of him, though, a very cheerful Martha opens the door.

'Oh, Kate dear, how are you? Come on in.'

'I'm great, Martha. How are you?' Every time she closes that door there is only one moment replaying in her mind, so she takes a deep breath and tries to think of the least sexual thing ever.

'Fantastic. I was about to have breakfast. Richard is in the bathroom.'

'Oh ok, I'll just wait here.'

'Sure! Want some tea?'

'I'm not that much of a tea girl, but sure, why not?'

Martha prepared two cups of tea and made a sign for Kate to sit down. The silence was awkward, Kate could hear the gas running, Rick was definitely taking a bath and as usual he was going to take his time. Memories of baths together came to Kate's mind and she immediately blushed, looking down so Martha wouldn't notice.

'So... Kate. While we're alone... May I ask you a question?'

'Of course, go ahead.' She knew something bad was coming.

'I know it's not really my place to ask this, and trust me I never mess around my son's business. I just... What exactly are your intentions towards him?'

'Martha, I...'

'I don't mean to sound worried, Kate. I was never that much of a mother to him, and I know my son can take care of himself. He was always a responsible person, even when he was in that… D. Juan phase. But truth is, Richard has had his heart broken several times. And I know for a fact that he never cared that much for anyone else, as he cares for you. I've seen him at his highest highs, thanks to you. But I've seen him at his lowest lows, Kate. I know how much heartbreak one can take, before one falls and never gets back up. I've seen that happening before. I just don't want it to happen to him. '

Kate took a sip at her drink, looking at the floor of Castle's living room. She could feel Martha's gaze trying to penetrate her mind, looking for the answers that she wasn't giving. After a few seconds Martha finally gave up and focused on her drink, still waiting for an answer.

'Kate I hope you don't take this the wrong way. I really like you, I know you are an amazing person and of all the women my son has been with, you are definitely the best one. Because, Kate, if you leave him, if you break that man's heart, he will never recover.'

She looked into Martha's eyes, ready to talk.

'Martha, I… I don't know how to answer you. I can't assure you that this is going to be forever. Everything ends. But on what depends on me, I am never letting him go. I've learned to love every single detail of your son, the crazy stories that he imagines at crime scenes that drive me mad; his immaturity, which I'm sure you know it's so hard to tolerate sometimes; the way he is, sometimes, inconvenient. But I also fell in love with his good side; the one he shows when he's with you and Alexis, the one where he's completely aware of his father duties and how much of a family man he is. Not to mention all the years that he stood by my side, all the things we went through as partners at the precinct, the times that he saved my life – and I'm so glad he did, because if it weren't for him I wouldn't be here sitting on this couch, having this conversation with you. I have accepted his good side and his bad side. I'm really sorry that I made him suffer, it was never my intention but I had too many things in my mind, in my life, that wouldn't let me be with someone the way I wanted to, wouldn't let me give myself with all my heart like he deserves. I'm a one and done kind of girl, Martha, and as time goes by I feel even more certain that he is, indeed, my one and done. I deeply care for your son, Martha. And for you and Alexis too. I'd be honored to be a part of this family. I love him with all my heart, Martha, and I'll do the impossible to make him happy. Even if it means walking away, if he wants me to. But if that happens, I'm not going without a fight. I love Rick, and I would very much like to spend the rest of my life with him.'

Martha smiled at Kate.

'Did you hear that?'

'Hear wha…'

'I did, Mother.'

Kate turned around to see a freshly bathed Castle standing behind her, leaning against doorframe of his study.

'How much did you hear, Castle?'

'Highest highs, lowest lows.'

'Crap.'

'I'm sorry for my mother.'

'It's ok; there isn't one thing I said that I didn't mean.'

'I'm glad.'

Castle leaned down to give her a kiss, and she couldn't contain her smile – he smelled like heaven. Martha stared at them with loving eyes, admiring their happiness.

'Oh, and don't worry Kate' he said, making his way to the kitchen 'If it's up to me, I'm never letting you go. You're stuck with me. I love you. Always.'