Disclaimer: I don't own Castle or Firefly.
Captain Gates knew there was something off about Richard Castle. She couldn't pinpoint what exactly, but she knew, in her gut, it was there. It was the way he held himself – many people passed it off as pride and superiority; after all, he was a best-selling author. But Victoria Gates knew it was something different, he walked with an air of… authority. Yes, the man held authority, much in the same way she did.
She'd caught a glimpse of it once. A newbie had yelled "Captain!" and run down the hall towards her. She'd been watching Beckett's team and had seen Castle stiffen when the boy shouted and then quickly recollect himself. No one else had noticed. At the time she had brushed it off as a quirk, but after a year of observation, she knew it was no quirk. The man was hiding something and she wanted to know what. Aside from the mayor, it was the reason he was still here. If this man was a threat to her city, she'd find out and take him down.
She had no proof though! One minor incident and a gut feeling was no proof – not even probable cause! She'd have to bide her time and be patient. And she would do what she must. She would wait.