Stana Katic
[WARNING: The following story contains spoilers from Monday's episode of ABC's Castle. Read at your own risk.]
On Castle, some of the ghosts from Detective Kate Beckett's past just won't stay buried.

Beckett (Stana Katic) was reminded of that in a big way on Monday's episode, when she was asked to go on a simple undercover operation to bust a drug ring. There was just one problem: Although Beckett was told she was posing as a drug courier named Elena, she soon learned that the person she was impersonating was actually an assassin! Although Beckett managed to maintain her cover long enough to carry out a "hit" (who knew items in your pantry could make fake blood so quickly!) the jig was up when Beckett came face-to-face with drug lord Lazarus — who just so happened to be Vulcan Simmons, a one-time suspect in Beckett's mother's murder.

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Once Beckett was identified, she was taken out to be executed. However, just before Simmons' henchman could kill Beckett, the real Elena came to her rescue, sparing Beckett's life at the behest of "Lazarus." But during a post-operation debriefing, Beckett learns that the drug money is being laundered to fund a heavyweight politician. Although the money is untraceable, Beckett knows who the real Lazarus is: Senator William Bracken (Jack Coleman), the man responsible for Beckett's mother's murder.

"[The episode] gave us a chance to re-mythologize Bracken," Katic tells "We wanted to reintroduce him to the audience in a way that would kind of validate the threat that we had set up for so many seasons."

Indeed, now that Bracken has saved Beckett's life — evening the score from when Beckett thwarted an assassination attempt against the senator last season — creator Andrew W. Marlowe says Beckett must think differently about how to proceed with Bracken. "They've had this détente because, to the best of Bracken's knowledge, Beckett has information that will sink him," Marlowe says. "But this means if something else happens in the future, if these two come into contact, the gloves are off. That Sword of Damocles hanging over her head has to give her a sense of unease."

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And while staying off Bracken's radar isn't impossible, Beckett's history doesn't suggest she will be able to bite her tongue forever. ""This guy, who is a form of evil in the world, is out there and may achieve the highest office in the land. That, in Beckett's mind, is morally repugnant," Marlowe says. "How does she handle that? In the back of her mind, there is a little bit of crisis. Those are things that she wrestles with as we sow the seeds for further storytelling."

However, Marlowe notes that Beckett is less likely to throw herself into the fire with Bracken thanks to her relationship with Castle (Nathan Fillion). "Does she go down the rabbit hole like she has the last four and a half seasons?" Marlowe asks, referencing the episode's final shot. "No, she takes Castle's hand and chooses to be with him instead of choosing to do something crazy. It shows some growth and maturity of the character."

And despite the danger Beckett found herself in during the undercover operation, the episode also reaffirmed the strength of the Castle-Beckett relationship. When Beckett realized she might not make it out alive, she wrote him a letter to make her feelings plain. "If something happens, if I don't make it, I need you to know that our partnership, our relationship is the greatest thing that's ever happened to me," she wrote. "You're an amazing man, and I love you with all of my heart. Always." Katic says she believes Beckett has always felt that way, but it was nice to finally voice it in an episode, both in the letter and again in person when they were reunited.

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 "I think everyone faced with their own mortality speaks their final truth, and her final truth is that she's completely committed and absolutely in love with him," Katic says. "We said it a long time ago that Beckett  [is] a one-and-done type. So, I think her committing to marrying him already speaks volumes to some deep rivers that are in that character. ... But this is when it's really important because if it's all over, he has to know that he was the love of her life."

While the couple's feelings for each other aren't in doubt, the renewed threat of Bracken certainly poses  questions about Castle and Beckett's possible "spring" wedding. "These two characters are really committed to each other; this episode shows Beckett's level of commitment to Castle," Marlowe says. "These are two characters that want to be together. But can stuff happen? Sure. Weddings can either go off without a hitch or they can be disastrous. We do plan to have one more significant bite at this Beckett's mother's mythology stuff before the end of this season. All sorts of things can happen. We still have a few tricks up our sleeve."