'Castle' 100th Episode: Nathan Fillion And Andrew Marlowe Preview 'The Lives Of Others'

The 100th episode of "Castle" may be airing on Monday, April 1 (10 p.m. ET on ABC), but it's no April Fools joke -- in fact, the consequences of the "Rear Window"-esque case could hit surprisingly close to home for our heroes.

At the cake-cutting ceremony for the milestone episode, The Huffington Post caught up with Nathan Fillion, creator Andrew Marlowe and other members of the show's cast to preview what to expect from the Hitchcock-inspired hour, which Marlowe described as "a champagne glass of an episode," designed with the series' most loyal fans in mind -- especially those who love Castle (Fillion) and Beckett (Stana Katic). Read on for what we learned.

• On coming up with the 100th episode: "One of things with the 100th episode is, we wanted to put the lens squarely on the Castle/Beckett dynamic, we wanted to do something that was fun, something that was basically a champagne glass of an episode -- it has a lot of sparkle, a lot of wit. So when [co-writer] Terri Edda Miller and I were conceiving it, we were looking for a story that would allow us to put the lens on our principle cast, instead of having a big thing that drew them all away. So putting Castle in the middle of this is kind of "the boy who cried murder." It's like Michigan J. Frog. When he's looking, he sees stuff, and when Beckett comes over, she doesn't. It allows us to recapture some of the great chemistry we had in the first season. We wanted to do the quintessential episode that could've played in any season. We're really pleased with how it turned out."

• On the plot of the 100th episode: "Castle is a witness to something heinous, but he's having trouble convincing his friends that there's something going down. There's something that stirs within you [in that situation] -- first of all, you have a bit of a 'really, you don't have my back?' moment, and then there's the moment of, 'Then I'll do it on my own, regardless of how I'm injured!' Those are real-life moments. Those are things that we can all relate to. We're not all cops investigating murders, but we all do have moments where you say to your friends, 'I can't believe you're not backing me up on this!' It's reality-based in that way."

• On his involvement in the 100th episode: "We have a really interesting episode. It's "Rear Window." The writing is very Hitchcock-esque, which is very cool, so it's a little different from what we usually do. Nathan's character becomes very helpless and isolated and he's separated from the team and he wants to help the team, but ultimately, he witnesses his own thing and he desperately needs the team, but the team's not there. I can say that my character, along with a couple of other characters, are instrumental in the end of the episode with bringing him out of what he's spiraling into. It's pretty crazy. It's gonna be a fun reveal."

• On what's ahead for Lanie: "Lanie is back to secretly seeing Esposito. She is possibly going to be doing some more scenes with Alexis [Molly C. Quinn] coming down to the morgue. We need to revisit that -- [that's] one of the things everybody wants to see. I want to see it too! It's time. There's so much going on and such little time because the season's coming to an end, but Andrew and the writers are working their butts off to make everything happen."

• On what's unique about the 100th episode: "I think that the 100th episode is going to be a surprise, in that we're gonna see Mr. Fillion in his element ... If you could be a fly on the wall, just you and Nathan, I think this'll be the experience you'll wanna have."

Tune in to the 100th episode of "Castle," "The Lives of Others," on Monday, April 1 at 10 p.m. ET on ABC.