The heart of "Castle" was always the bantering, exasperated sexual tension between crime novelist Rick Castle and police detective Kate Beckett. It's not all that surprising, then, that their first kiss actually happens while on a case. Trying to keep a suspect they're tailing from figuring out what they're up to, Castle pulls Beckett into the classic "fake-out makeout." The reasons may be fake, but the feelings the kiss stirs up are very real.
Season 3, episode 13