Let's rewind the clock to CastleSeason 4, Episode 16, "Linchpin." Sophia Turner, the backstabbing CIA agent on whom Castle based his character Clara Strike, drops a wicked bombshell just before she is gunned down.
"You don't think you gained special access to the CIA back then because of your charm," she says, implying that Rick's dad — whom he has never met — is somehow affiliated with the agency.
When Castle looks up at her confused, she replies, "You really don't know, do you? Guess you never will."
According to show creator Andrew Marlowe, there's a distinct possibility that Castle's father will resurface in Season 5 — but only if the storyline appears organically.
"We know there's a big burden on it, and we want to get it right," Marlowe told TV Guide.
"It promises great potential in storytelling and allows us to recontextualize Castle a bit and get some more insight into him. But until I have something I'm 100 percent happy with, it's a hesitation. I'm trying to find the most fruitful path emotionally for our characters."'