A/N This story is set sometime in the future of all three cannons, where both the Brennan-Booths and the Castles are married. It also assumes that Olivia is still with Cassidy, though they are not married. In terms of the SVU element of this story, it's an E/O fic.

For my sister by choice, Sarah

Olivia Benson sits across from Kate and Rick Castle, smiling through weary eyes at the young couple's light banter. They're relentless in their teasing, but it's clear to her that they deeply love one another.

It's refreshing to see how carefree they are, how even in the toughest of times on this case they've been working jointly, Rick has made Kate laugh. It makes the older detective's aching own heart slightly lighter to be around them, and for that she's grateful.

The FBI is working with both her and the 12th precinct on this case as well and it amazes her how different the Castles are from the Booths, or rather the Brenanan-Booths, a team who've come in from DC to offer their unique insight on cracking cases using only the skeletal bones that, sadly, are all that remain of the 1-6's victim, a victim whose murder looks like it ties in with some of the 12th's open homicides.

Shaking off the wave on melancholy that threatens to overwhelm her on behalf of the victim, she forces her thoughts to focus on happier things and, with effort, laughs inwardly at the absurdity of the fact both of the teams she's working with are, in fact, couples.

Again, the differences between the Brennan-Booths and the Castles strike her. Temperance Brennan is a brilliant scientist, but her speech has a stilted edge and though, Olivia can't put her finger on why, she knows that the woman's husband, FBI Agent Booth, he's never introduced himself as anything else and Olivia hasn't pushed, tries to do more than just lighten the mood when he jokes, he's giving his wife social cues. Cues she truly seems to need to guide her through interactions. Olivia admires that Agent Booth is willing to help his spouse navigate the world this way and only hopes that the slightly cocky and rigid thirtyish couple can find enough happiness to continue to make a life together despite such disparate personalities, both for their own sake and for the eighteen month old girl at home that neither of them can stop adorably mentioning.

"So Olivia," Kate Castle says conspiratorially, learning toward the older woman's side of the table and breaking her from her thoughts, "Do you have a partner?"

Olivia hesitates, knowing what the younger woman is truly asking. She considers for a moment telling them about Cassidy, but something in her heart pulls her in a different direction. "I did for twelve years," she begins. "He was tall, intense, with piercing blue eyes, dedicated to the job and to the victims. He was gentle with his kids and with me. We loved each other very much, though we were never as playful as the two of you. We were always too worried about the other one getting hurt, killed or disappearing from the desk across from us before we were ready to say goodbye."

"What happened to him?" Rick Castle asks, the soft timbre of his voice denoting concern

"He disappeared from my life... but not from my heart. For better or worse, he'll always be the only partner that truly matters."