Ryan reveals a secret past and goes undercover with Irish gangsters on Staten Island.
- Amicable Exes: Siobhan and Ryan fall into this after some things are cleared up. When she asks if any of their time together was real, he assures her his feelings were.
- As the Good Book Says...: Bobby S references the Prodigal Son and quotes the biblical passage when welcoming 'Fenton' back into the crew.
- Becoming the Mask: Not to a dramatic degree, but emphasis is placed on how Ryan has to do more than just call himself ‘Fenton O’Connell’ when resuming his old cover identity for the current case, he needs to get fully back into O’Connell’s old mindset. When he apologizes for arguing with Esposito while undercover, the latter waves it off as being not his fault since he was in character.
- Big Damn Heroes: The case concludes with Beckett and Esposito getting one when they respond to Ryan’s earlier call for help in time to save him and Siobhan from being executed in a shooting, Ryan giving them both a dramatic introduction that’s only slightly undermined when he introduces Castle and the unarmed Castle awkwardly steps out and explains that he didn’t bring his vest.
- Dark and Troubled Past: Castle initially wonders if they’re seeing a seedier side to Ryan when they learn that he was friends with a mobster and dated a woman affiliated with a gang, but it’s downplayed when Ryan reveals he was ‘just’ undercover a few years ago.
- A Day in the Limelight: For Ryan. He used to run undercover with the Irish mob and had a girlfriend named Siobhan.
- Hidden Depths: The younger of the Team Kids Ryan used to be an undercover cop in the gang unit and boy is Fenton O'Connell scary.
- Important Haircut: Ryan gets a close shave when he goes back in as Fenton.
- Lady Macbeth: The killer was Maggie who wanted her husband to ascend the throne, so to speak.
- Law of Inverse Fertility: Ryan and Jenny are taking fertility tests. They can't get pregnant. Because they're already pregnant.
- Mood Whiplash: When Ryan introduces his back up to the gangsters, Castle's entrance doesn't exactly fit the mood:Ryan: Yo Javi, where you at?!
Esposito: [Beat] Right here, bro!
Ryan: [as the Irish boys turn on Javi] Oh, no, he's former Special Forces, you don't wanna pull on him. You wanna meet the rest of my crew? Hey, Beckett!
Beckett: You called, Ryan?
Ryan: Don't let the looks fool you, boys, you don't wanna mess with her either. Castle!
Castle: Seriously? I didn't... I didn't bring my vest.
Ryan: Drop your weapons, now. - MacGuffin: The Bible, a book full of evidence that could put Bobby S and his gang away for good.
- New Old Flame: Siobhan O'Doul is this for Ryan. Or, more precisely, his undercover alter-ego, Fenton O'Connell.
- The Reveal: We finally learn why Castle became a writer in the ending: In boarding school, he was about to fail a class and paid someone to write a paper for him. The teacher was deeply impressed by the work and called it great literature. Since then, he became a writer in order to be worthy of the praise he was given.
- Took a Level in Badass: Kevin Ryan shows us all how he made detective and survived a couple years undercover in organized crime. Take a look at Mood Whiplash and see how he faced down a trio of angry, armed Irishman with nothing more than his charm, his partners, and his giant, swinging chinbones.
- Was It All a Lie?: Siobhan asks Ryan if any of their relationship was real late in the episode. He assures her that his feelings were real.
- Wham Line: "We took all those fertility tests for nothing. Because I'm already pregnant."
