'Castle' Boss Previews 'Emotional' Season Finale: 'Everything May Change'

Castle Season Finale Andrew Marlowe Inset - H 2012
Vivian Zink/ABC;Getty Images

Castle Season Finale Andrew Marlowe Inset - H 2012

It may be four seasons in the making but as Castle creator Andrew Marlowe says, the dynamic between partners-in-crime Richard Castle (Nathan Fillion) and NYPD detective Kate Beckett (Stana Katic) will drastically change by the end of Monday's "emotional" finale.

With the mystery of the murder of Beckett's mother rearing its head again, Castle's secret -- that he has been withholding vital information that could help move the cold case forward -- is about to surface. 

"We've seen one of [their] secrets come out and in the finale, the other secret comes out. There's recognition that [Castle and Beckett] both, in a way, have been lying to each other," Marlowe tells The Hollywood Reporter. "We get to some explosive moments that force them, really for the first time, to confront everything they've been feeling out in the open."

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Marlowe reassured viewers that things will be more black and white with less subtext, the latter of which the ABC crime procedural has become known for. "They've never really sat down and talked about it," he said. "This is an episode where all of that comes out and it's a case where not everybody has the same point of view on what should be done and who should be told about it and what information should be withheld."

By the final moments of the episode, "Always," "we end up at a place where professionally and personally, everything may change," Marlowe said.

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So much so that the synopsis alluded to potential shifts in the precinct. When asked whether certain people may be out of the precinct by the conclusion of the finale, Marlowe remained coy. "That's not something I will advertise before the finale. Let people watch and see what we're doing," he said.

According to Marlowe, "firm decisions will be made" on where Beckett and Castle stand on their partnership (and nonexistent relationship) when season four ends: "They have to deal with the consequences."

Castle airs its season finale Monday at 10 p.m. on ABC.