Set between S4 and S5. Gen fic, but could be crack pairing if you squint really, really hard. It's based on this S/V exchange in "Prophet Five":
"Sydney: You're waltzing!
Vaughn: Yup. I've been practicing for our wedding.
Sydney: With whom?
Vaughn: Weiss."
Hope you enjoy. :)
(
Shall We Dance? )