"Castle's" biggest bad -- Senator William H. Bracken (Jack Coleman) -- returns Monday night, and Beckett might finally have a chance to lock up the man responsible for her mother's murder.
"He's a really bad guy," Coleman told The Clicker about his archvillain character. "But like all bad guys, he justifies his behavior. … He tells himself that he's in very murky world, and that you can play by the rules and be a sap, or you can grow a pair and do whatever has to be done."
The question in "Recoil," Coleman noted, is "how far Kate (Stana Katic) is willing to go to exact the vengeance that she can just taste."
"It is very much a sort of Ahab in search of the whale," he added, comparing Kate's obsession to that of the "Moby-Dick" sailor.
"(Bracken) seems to land on a plate right in front of her, but it's just not that simple as it turns out," shared "The Heroes" alum. "And now she really has to wrestle with what's she's willing to do, who she's willing to be.
"She just wants it so badly and she really has to wrestle with what she's willing to do."
So does Kate's obsession threaten her new romance with Rick (Nathan Fillion)?
"Castle to Beckett is light and love and life," said Coleman. "And Bracken's the opposite: he's darkness, he's death, he's everything bad. But it is yin and yang, and they both have a hold on her.
"When you have something that's burning a hole in your soul and then it's right there in front of you and you have a chance to really act on it and get your pound of flesh, what do you do? How do you do it? I think inevitably it affects their relationship because it's the dark side that pulls her away from him … and it does take a toll on her."
"What does Ahab do when she finds the whale?" Coleman mused about Kate's quest. "Will the whale kill her -- drag her down and drown her?"
"Castle" airs Mondays at 10 p.m. on ABC.
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