Get ready to see a much different side of Richard Castle.

On Monday's Castle, the usually goofy mystery writer is all business as he searches for Beckett (Stana Katic), whom Castle (Nathan Fillion) believes was abducted by serial killer 3XK/Jerry Tyson (Michael Mosley) and his disciple Dr. Kelly Nieman (Annie Wersching).

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"We've always really liked what 3XK and the Jerry Tyson character did for the show," executive producer David Amann tells "3XK and Jerry Tyson have cast a long shadow over the episodes they've been in, but in most cases his actual screen time has been somewhat limited. We were really hungry to get a bigger bite at Tyson and have Tyson and Castle, and Beckett interact more directly."

Even though Castle is sure Tyson is behind Beckett's disappearance, there's just one problem: Tyson and Nieman were both at the 12th Precinct when Beckett went missing. "Is the person we're dealing with really Tyson?" Amann says. "I think the audience is probably with Castle in [believing] that this guyis Jerry Tyson, and he playing a game. But there remains an open question as to whether that's actually true."

In order to find Beckett, Castle will somehow have to prove he's right. But that also involves a waiting game that Castle doesn't believe he has time to play. "Beckett is missing, and there is a tremendous urgency with Castle to try to find her," Amann says. "This is his wife, and [Tyson] is a guy who Castle's well-acquainted with, in terms of past history. He's ruthless [and] we can assume he is going to do the worst. Castle's going to do whatever he can to try to stop that and affect Beckett's recovery."

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But just how far will Castle go? After all, by taking the law into his own hands, Castle might be playing into Tyson's. "You saw a bit of this in [Castle] in the two-parter when Alexis was taken," Amann says. "He was ready to do damage to people because the fate of his loved ones are at stake. The same is true here. This is the love of his life, and that's going to make a man do questionable things."

Castle airs Mondays at 10/9c on ABC.