It was completely out of the question that she was going this year. She'd always refused to go, every single year and every single year she ended up being there anyways. Sometimes the boys had dragged her there even though they were working on a case at the time, they just didn't care and once she even went because she had to see what (or more specifically) who was there as well. She could never blame the boys for wanting a little bit of fun and she had to confess, Castle's Halloween parties really were the best but this year, no, this year she just really couldn't and wouldn't go.
Just imagining it gave her a terrible headache.
Up until now everything had gone perfectly smooth. Well, almost. Their relationship was still a secret. That was, if she didn't consider Alexis and Martha knowing about it.
That said, they had been in some really precarious situations more than once and the boys as well as Lanie knew that she wasn't single anymore. She was actually surprised at how well Castle was dealing with it, he chimed right in whenever the boys started teasing her. He always paid for it later though. And with that trip to the Hamptons they actually both paid for it. Damn that case, now Ryan knew and Kate had no idea for how long he would be able to keep quiet about it.
The Halloween party might be a trigger for him to spill the beans or he might just drop a stupid comment that would give their secret away. She knew it he might do that accidentally. It was Ryan after all but she didn't want to risk it.
It wasn't like the boys didn't know Castle's loft as well, they'd been there often enough to know their way around. But everyone got familiar with a place after a certain time. You could actually see by their behaviour if they were living in a place or not. And Beckett…she'd definitely been living at Castle's loft. They stayed at her place often enough but Kate had noticed herself how differently she behaved whenever she was in the loft. She and Martha had a different way of talking to each other, she felt comfortable in every corner of the flat and the worst part if the boys or Lanie came over, there were a lot of her toiletries in the bathroom. Yes, it was Castle's en-suite but during a party the toilets tended to be used, and not just the guest toilets. And she was almost certain that she'd lost a pair of earrings somewhere in the living room and Castle hadn't found them yet. Lanie would recognise them and even Esposito would get suspicious.
"Come on, Kate! You have to come!" he begged her again with puppy dog eyes and pulled her out of her thoughts.
"I told you already, Castle, I won't. There's no way in hell that I'll come this year."
"But they'll suspect something if you're not here. What reason could you have to be somewhere else?"
"I am having a horror film night with my boyfriend. Ryan won't tell on us and Esposito will believe it because he knows I actually do have a boyfriend."
"Can't you humour me then? Or my mother? She was so looking forward to this."
"Try as much as you like, I am not coming. Now drop it or you won't get anything from me anymore tonight."
Castle grumbled but said nothing more about the matter. He was sure he'd find a way to convince her even if it took him till the last minute. For now he stayed silent though because he really didn't like spending the night alone anymore.

The bad mood started three days later. The invitations for the Halloween Party had been sent out ages ago. Okay, maybe just two months ago but still. It always took some people a very, very long time to RSVP. Some however, had already given their yes.
It was lunch time when he got the call. One of his regular guests had to cancel. His mother, who lived in Europe, was ill and he had to go over to see her and wasn't sure when he'd be back. It was past 2pm when he got another call. Another regular had to cancel because her very new boyfriend had a weekend trip planned for them and she didn't want him to cancel that because their relationship was so new. By the end of the day he had received 5 cancellations. 5 bloody cancellations in one single day. It really put him in a bad mood and not even Beckett managed to cheer him up.
"It's like the first day of bad luck! And it's your fault too!" he moaned at her, almost hanging over his chair in the precinct, drawing a long face.
"How is it my fault?"
"Yesterday! When we went to the crime scene, remember?"
"Oh. Come on, Castle, you can't be that superstitious."
"Well, I am. You made me walk under that ladder even though I didn't want to!"
"There was no other way to go and we were in a hurry."
"It's not like a dead body is going anywhere, now is it."
"Alright, fine. If you want to blame me, blame me, but I have nothing to do with this. Maybe this just isn't the year. Maybe –" she said and after quickly looking around leaned in closer to him, finished her sentence "- this is the year where we can spend a scary horror movie night together without a party."
He smiled a little at that but it didn't satisfy him.
"I call it my first day of bad luck anyways. Bad luck from walking under a ladder."

On the second day of bad luck it was rather quiet. No one cancelled, no one agreed to come either.
Beckett managed to keep Castle occupied by giving him tasks that would help solve their current case and by the end of the day, they had another scumbag locked up safely behind bars and the boys were joking around about Castle's misery. Ryan told Castle he couldn't make it which was when Castle moaned about being cursed again.
"You gonna have to find another magician to un-curse you?" Esposito asked with sly grin but Castle ignored him.

Day four and five weren't very eventful either. Some people had the courtesy to call and tell Castle that they couldn't come. Alexis was home over the weekend and kept her father's spirit up by making jack-o-lanterns and getting some decoration ready that she could hang up in her room at the college dorm. Beckett had her own means to keep Castle's spirit up during the night.

On the sixth day, Castle was seriously getting worried. He had not even had one single guest RSVP-ing, not a single one – except for the ones who cancelled again. He had no idea why – except for the fact that he walked under a ladder and had bad luck for the rest of his life – and he didn't know what he would do if no one came. Or if just one person came and he'd have to tell them that the party was cancelled completely.
He had a hard time concentrating at work and when a new homicide was called in he couldn't focus. Whenever Beckett asked what he was thinking (about the case), he'd get out a new theory of why no one came to his party.
"Do you think they didn't like Frozen Heat and they don't want to tell me so they're avoiding me?"
"No Castle, your book was brilliant as always. Now focus."
"But what if they think this year's theme was too appalling?"
"What is this year's theme?"
"None really…Marvel maybe…"
"Whatever it is, stop wondering and help me solve this case."
"Only if you help me figure out why no one's coming."
"Fine," she replied just to make him shut up about it for a while.

The days passed by but Castle still couldn't find a reason why no one was coming. There were only three days left till the date of the party (it was obviously going to take place before the actual Halloween because some of his guests had kids and they had to go trick or treating on the 31st) and he was now thinking about alternative plans for the night.
Beckett kind of enjoyed watching him being so worried over a tiny little party, it was fun. But then, she did know how much it actually meant to him. So that by Friday evening after solving another case that allowed them to have their Saturday off, she invited him for drinks and brought the boys and Lanie along. Both Esposito and Lanie had cancelled during the week. Castle had been absolutely gutted.
"You always come to my party! Even if you're working on a case!" he'd said and had gotten a wave of apologies that didn't quite satisfy him but he eventually just stopped arguing and sulked away.
Now they were having some drinks together and it seemed like Castle had forgiven them again.
The night wore on and soon one after the other left so that only Castle and Beckett were sitting at the bar.
"Now you don't even need an excuse not to come. I am so very disappointed in all my guests. How could they do this to me?"
"Next year, Castle. We can do it properly then. But for now, let's just enjoy a nice weekend off."
She drowned her drink and took his hand.
"Come on, I've got something for you," she added teasingly and together they went to her apartment.

She'd found his costume for the night – Captain America – during the week and had smuggled it to her place. She'd found an Elektra costume for herself – there was no harm in teasing him a little bit – and she was about to show it to him. Her plan was to convince him to just have a little party themselves at his place but only after a peaceful day at her apartment.
When she told him, he was over the moon about the idea of having a private party and even more so about her costume. They spent all of Saturday morning in bed, went for a walk in the park during the afternoon and got themselves ready for a private party in the evening.
What they didn't know, was that the loft was occupied.

There was actually no reason for them to be dressed up since they were having a private party but Beckett liked to tease Castle ever so often and dressing up just happened to be one of the things which drove him crazy. And she had fun too.
She was wearing a black coat over her costume – which she did cover up a bit because it would've been a bit too showy – and Castle kept trying to get the coat off her in the elevator.
When she'd seen him in his Captain America outfit first she wasn't sure whether it was better to laugh or to admire. She did both.
"Why didn't you go for Iron Man, wouldn't that have been better for you?"
"Why, because of our similarities? Ruggedly handsome, rich and creative?"
"And served with way too much ego, yes."
"There are no good and half way comfortable Iron Man costumes out there that look authentic and building one was too hard…"
It had made sense to her. And she liked him as Captain America. And it was hard to resist Captain America.
"Will you just leave it? We're not even in the loft yet."
"That hasn't bothered you before…"
"Yeah well, I wasn't wearing a red leather costume then."
He grinned at her but did give in and just held her hand.
The elevator opened, the two of them got out and went to the door. There, Castle spun her around and kissed her fiercely and she kissed him back for a moment but then remembered something and tried to stop the kiss but it was already too late.
"KATE?!" she heard the very surprised voice of her best friend and the gasps from several people who stood behind Lanie who had opened the door, wanting to scream "Surprise" at them.
Castle had immediately let go of Kate when he heard her name but it was too late. They knew. Not all of them but enough.
"What is going on here?!"
"Hi dad…" Alexis peeped around the door and looked at a very flushed Kate Beckett and an utterly surprised Richard Castle.
"It was supposed to be a…well…prank and surprise…I guess the surprise is on you though," the girl answered her father's question.
"What kind of prank. What is going on, what are all these people doing here? They all said they couldn't come?" Castle was really confused now and looked at Kate who – even though she was feeling really hot and sweaty and uncomfortable because her friend kept staring at her in disbelieve – had a hard time not to start laughing.
"I'm sorry Castle. This was supposed to come out a bit differently. Alexis called me a while ago. She had this plan of getting back at you for the Zombie outfit and every other prank you ever played on her and she needed my help. I stole your guest list and gave it to her and she and Martha called everyone to cancel and RSVP to them instead."
"You let them make me believe that I was being haunted by bad luck for walking under a ladder just so they could prank me?!"
"Yeah."
"Oh Kate, I love you."
She blushed again and hoped no one but the people at the door – Lanie, Esposito, Ryan, Martha and Alexis – could hear.
"Well…it didn't quite have the effect we intended."
"Oh, you did great. I really believed I was having a streak of very bad luck."
He finally stepped into the loft, hugged his daughter and then looked around to see who was there.
Almost everyone who was ever invited was there, filling every bit of space and looking fantastic in their costumes, drinking and finally, starting to talk again. Castle went and played the lovely host, laughing about how his family tricked him and making sure about who had seen him and Kate kiss. Beckett told Lanie to not say anything for now because she wanted to enjoy the party and her friend obliged with a serious frown on her face – as did Detective Esposito.
In the end, all she wanted was to have a bit of fun. The fact that their secret was out, didn't matter that much anymore.
"She even managed to make you come after all," she heard him whisper into her ear at one point and she laughed.
"She is your daughter after all."