On Monday's Castle, Detective Kevin Ryan will get a blast from his past.
When Castle (Nathan Fillion) and Beckett (Stana Katic) investigate a murder that leads back to an Irish crime family Ryan (Seamus Dever) once infiltrated as an undercover narcotics cop, he must step back into his old persona in order to bring the family down.
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In the process, viewers will meet Siobhan O'Doul (guest star Cara Buono), a bar owner with whom Ryan had a relationship during his undercover days. And based on the exclusive sneak peek below, this isn't exactly a happy reunion. "You didn't even have the guts to tell me to my face. Just a note on the dresser," Siobhan says from the wrong side of a holding cell after learning Ryan's true identity. "Well, at least you're Irish. You didn't lie about that."
"I didn't lie about a lot of things," Ryan replies. Indeed, it seems whatever feelings may have existed in the past were real. That fact won't sit very well with Ryan's wife when he goes undercover once more to help his former flame.
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"It cuts close to the bone," Dever tells TVGuide.com. "He can't explain [everything] and he doesn't want to scare [his wife] and tell her that he's walking back into the hornet's nest."
But will Siobhan even want Ryan's help? Watch the clip below.
Castle airs Mondays at 10/9c on ABC.