Disclaimer: Neither Castle nor BtVS belong to me, they belong to Andrew Marlowe and the inconquerable Joss Whedon respectively.
They were in L.A. to catch Mike Royce's killer and had just cracked the case. Rather than heading baxk to the hotel as planned when the case was over Castle had dragged Kate to a karaoke bar the moment they'd closed the case. She'd argued but Castle only laughed and pointed out that technically they were on vacation and she'd caved.
Once in the bar she gave Castle an inquisitive look. There were more than a few normal looking people but they were outnumbered by what had to be people in all kinds of costumes. "What kind of bar is this Castle?"
"A bar full of people like me," Castle replied with a small, almost hesitant smile.
Kate didn't know why the normally exuberant writer was so subdued but she didn't like it. Gripping his arm she held the taunt that might have leapt from her lips and gave the wonderful man who was her partner a warm encouraging smile.
Castle shot back a thankful grin and looked away, his eyes scanning the room till he found the person he was looking for. His grin widening and he shot through the fairly packed bar, pulling Beckett along behind him. Reaching the end of the bar he drew the attention of a green man with red around his eyes and redish horns. "Lorne! Long time no sing."
The green man, Lorne, laughed, "Long time indeed, tell me is this-"
"The N.Y.P.D. detective I was telling you about," Castle interrupted with a nod. Lorne gave a questioning look and Castle shook his head. Kate frowned, something was going on and she didn't understand it.
Lorne gave an exaggerated sigh, "Castle, I simply must hear you sing!"
Kate's brow furrowed, "What do you mean? Castle can't sing."
"Rick! You've been hiding that voice of yours again!" Lorne admonished, "Get up on that stage and sing!"
"I'll sing with you if you're chicken Castle..." Kate taunted drawing an easy grin from her partner.
Eyeing Lorne's smug grin Castle turned his attention back to Kate, "I am so not chicken but I'll take you up on that anyway."
Walking over to the selection book Kate started flipping through it. Castle grinning over her shoulder just waited. A couple moments passed before Kate grinned and keyed a number into the selection board and pulled Castle onto the stage. Her eyes kept their twinkle as a distinctive opening guitar segment made her partner grin and raise an eyebrow. Nevertheless he opened the song right on cue.
I was walking down the street,
When out the corner of my eye
I saw a pretty little thing approaching me.
She said "I've never seen a man
Who looks so all alone,
Could you use a little company?
If you can pay the right price
Your evening will be nice,
And you can go and send me on my way."
Beckett had predictably taken over at 'She said' and was looking right at Castle, inwardly both hoping he got the message and shocked that she was hoping it so much.
Then it was Castle's turn again, his smile becoming wider as they got closer to the chorus, which he assumed was the reason Kate had chosen the song.
I said "You're such a sweet young thing
Why you do this to yourself?"
She looked at me and this is what she said:
Despite the line before saying she said both detective and writer sang the next lines, their voices harmonising.
"Oh, there ain't no rest for the wicked,
Money don't grow on trees.
I got bills to pay,
I got mouths to feed,
There ain't nothing in this world for free.
I know I can't slow down,
I can't hold back,
Though you know, I wish I could.
No there ain't no rest for the wicked,
Until we close our eyes for good".
It was Kates turn to sing the narrator's perspective, her eyes still focused on Rick, wait when did she- Later! She admonished herself as she sang.
Not even fifteen minutes later
I'm still walking down the street,
When I saw a shadow of a man creep out of sight.
And then he sweeps up from behind
And puts a gun up to my head,
He made it clear he wasn't looking for a fight.
Castle smoothly picked up as Kate neared the next 'He said' moment. Kate was mildly surprised at how easily they were working together.
He said "Give me all you've got
I want your money not your life,
But if you try to make a move I won't think twice."
As expected Kate elegantly picked up her line.
I go like "You can have my cash
But first you know I got to ask
What made you want to live this kind of life?"
Once again the pair sang in harmony turning out to the bar, sitting there in awed silence, and began the chorus.
He said "There ain't no rest for the wicked,
Money don't grow on trees.
I got bills to pay,
I got mouths to feed,
There ain't nothing in this world for free.
I know I can't slow down,
I can't hold back,
Though you know, I wish I could.
No there ain't no rest for the wicked,
Until we close our eyes for good".
Castle took the reins for the final narration.
Now a couple hours have passed
And I was sitting at my house,
The day was winding down and coming to an end.
So I turned on the TV
And flipped it over to the news,
And what I saw I almost couldn't comprehend.
I saw a preacher man in cuffs he'd taken money from the church,
He stuffed his bank account with righteous dollar bills.
But even still I can't say much
Because I know we're all the same,
oh yes we all seek out to satisfy those thrills
The last chorus was practically belted out both New Yorkers grinning as they sang. Kate couldn't quite remember the last time she'd had such a fun time.
"Oh, there ain't no rest for the wicked,
Money don't grow on trees.
We got bills to pay,
We got mouths to feed,
There ain't nothing in this world for free.
I know we can't slow down,
We can't hold back,
Though you know, we wish we could.
No there ain't no rest for the wicked,
Till we close our eyes for good."
The bar erupted in applause as the song ended. Castle gave a bow with his usual exaggerated flair and Kate simply laughed and left the stage, Castle close behind, as they went back to the end of the bar where an emotional Lorne waited as he dug a card out of his shirt pocket. As they reached him he held the card out to Castle. "I knew I'd need this today but didn't know why till now. Take this, call that number and tell them you have a code May and need the CSO immediately. Go, now. Call from the bathroom." The green man ordered, Castle's eyes widened but he nodded and headed off as ordered.
"What's going on?" Kate demanded from Lorne as Castle moved away.
"How much do you want your mother avenged?" the green man answered. When Kate was about to angrily respond he interrupted before she could open her mouth. "No, Rick didn't say anything. I have a gift you see. I can see a person's fate if they sing for me. You aren't in a costume bar Kate Beckett. Every person in this bar either is a demon or knows the supernatural is very real."
"That's rid-"
"Ridiculous? Is it really? Go ahead look closer at me. A trained detective like yourself should be able to tell it's no makeup job, and you can definitely tell I'm not lying."
Kate stared at him for a moment before panic set in, he was telling the truth. He was a demon! Then the part of her that trusted Castle implicitly slapped the rest of her upside the head and reminded her that Castle clearly knew this Lorne and would never lead her into danger. "Is Castle..."
Lorne headed Kate off at the pass, "Castle isn't a demon no. His kind evolved much like humans did. He's fae, specifically half siren and half seniatta. He can't do the whole super-whistle other sirens can though, all he gets from that half of his ancestry is a great ability to sing. The seniatta half though, that's a place he derives a lot of gifts from, I'm sure you've noticed some of your suspects being even more helpful with him in the room."
"Has he ever..."
"Used his ability on you? No, Rick refuses to use his ability for selfish reasons. Besides, he can only make someone do something he wants, he can't touch emotions," Lorne smiled, then eyed his watch, "Speaking of Rick, there he is."
Sure enough Rick was heading their way with a short blonde. As they reached the bar the blonde spoke, "So Lorne, what's the what?"
Lorne smiled at the blonde's unusual language, "Her mother's killer is about to pull a Wilkins, only with DC instead of a town like the 'Dale. I believe it's Senator Bracken of New York."
The blonde swore, "Shit, we had chatter something big was gonna go down in DC... This is bigger than we thought though and the Wilkins tactic ain't gonna help here, can't explode the senate."
Kate's eyes widened, "Wait what?"
Blondie cast an eye on Kate, "How much does she know?"
"Not much."
"I know Castle is half siren and half seniatta," Kate spoke.
Sighing the blonde looked at her, "I am what's called a Slayer. Specifically I'm The Slayer, I'm what the darkness fears. It is my destined duty to protect the people of this planet from the more evil examples of the supernatural. The man who killed your mother is a warlock attempting what's called an ascension, a transformation into a pure demon. I'm going to stop him."
All Kate could ask was, "How?"
"He'll need to die. Buffy," Castle spoke up, pausing to indicate the short blonde, "or one of the other slayers will kill him. Ascensions are bad news."
Kate nodded, taking a moment to think about that, she had always wanted to drag the man responsible for her mother's death into death row herself after being involved in every single step of his persecution but the supernatural wasn't something she was familiar with. "Can... can you do something for me?" She paused to look into Buffy's eyes, "Could you tell whoever... does it to tell him Johanna Beckett's daughter says hello, before he dies?"
Buffy's face grew a grim smile, "I'll tell him myself."