When the murder of an Irish gang member forces Detective Ryan to confront his somewhat murkier days as an undercover cop running with the Staten Island Mob, one of New York’s finest [dressed] will be forced to become one of New York’s most undercover to solve the case. In other words, tonight’s ninety-ninth episode of CASTLE is one Seamus Dever won’t soon for get and not just because it’s one away from the hit ABC series’ one hundredth [More on that later!] Or at least that’s the distinct impression we were left with following a recent one-on-one with the boy in blue who was only too happy to preview tonight’s pivotal episode, tease how said aforementioned episode affects his character’s marriage and reflect on his most memorable moment throughout the show’s hundred. See for yourself, after the jump.
Seamus Dever: Oh yeah. Ever actor wants to be the best advocate for his character, find their backstory and let some of it come to life. So as the series has continued, it has been really nice to break out of the utility role that you play almost every day and delve deeper into Ryan’s backstory. Which is the case with tonight’s episode that involves links to his past as an undercover cop in the Staten Island Mob where we get to find out a lot more about Ryan than probably most of us has ever known.
How little Beckett and Castle are in it! [Laughs]. It’s one of those things where everything is told through Beckett and Castle and how it affects their relationship. And I’m glad after ninety-nine episodes, they trust the supporting actors to carry a lot of that weight. But in terms of Ryan specifically, it was interesting to find out that he used to be a bit rougher around the edges. Much more so than a guy who wears three piece suits all the time.
Ryan is the one guy in the precinct that has settled down, married and is on his way to having children. Unfortunately, this episode really does shake up the foundation of that marriage. Ryan’s wife Jenny [played by Dever’s real-life wife Juliana] isn’t pleased that a women from his past [played by MAD MEN’s Cara Buono] has returned. She’s left wondering who she is, why Ryan has to go back undercover and what does this mean for their future? Ryan is going to be tested as he attempts to make amends for what happened seven years prior and dole out some justice.
I think the episode where I proposed to Jenny, it was just a really honest truthful moment that I got sort of swept up in. I look back at those few seconds and think that was just pure truth, something that an actor always strives for. That — and the laughter between takes, which is an everyday occurrence on a show like CASTLE — is probably my favorite moment.
Ryan… Because he has a better budget because ABC pays for it! I tend to be a lot more casual than Ryan actually. It used to not be that case, but now Ryan has far outclassed me with his Bespoke suits. I think I have five suits in my wardrobe so it’s got to be Ryan! 
New episodes of CASTLE airs Mondays at 10PM on ABC (CTV in Canada) and stars Nathan Fillion, Stana Katic, Susan Sullivan, Molly C. Quinn, Jon Huertas, Tamala Jones, Seamus Dever and Penny Johnson. Catch up with past episodes you may have missed for free online at clicktowatch.tv.