I've already spoiled that Castle has tapped James Brolin to appear in the second hour of Castle's two-part event on February 25th in, "Hunt".
Executive producer Andrew Marlowe is keeping details secret but says,
"There will be a moment between father and son when Castle comes to a realization and the two men confront the realities of their relationship."
Molly Quinn will also shine in this emotional episode when her character, Alexis, gets kidnapped.
"She tries to escape any way she can but keeps getting thwarted," Quinn says. "Near the end, Alexis kind of falls apart."
Marlowe says Fillion lets the tears flow as he portrays the powerless dad who fears for his child's life.
"We're giving Nathan the opportunity to show some colors and tackle a range of emotions he doesn't always get to show," says Marlowe, hinting that Castle's father figures into the kidnapping "in a very interesting way. He has a strong hand in how everything gets resolved."