The discovery of a young hacker's body in his apartment leads to the uncovering of a much more sinister plot, and the return of a familiar face.
This episode contains examples of:
- 2-D Space: Averted. While tracking the "Kingfish" Wi-Fi network from which the spy list is supposed to be downloaded, Castle and Beckett realize (with a reference to Star Trek II: The Wrath of Khan) that the router might be on a different floor when the signal suddenly weakens near a staircase.
- Agonizing Stomach Wound: Jackson got shot in the stomach while investigating Gemini and he goes to Castle's apartment for help pulling the bullet out.
- Balcony Escape: Knowing he'll need to rescue Castle and Beckett from Gemini's trap, Jackson escapes out the window after sending Martha away for some juice.
- Big Damn Heroes: Just before Gemini is about to begin torturing Castle for all he knows about the plot, Hunt distracts him, stabs him in the gut, and then shoots him to finish his job.
- Big Eater: Though Castle loves the finer things, he's also a connoisseur of carnie food and identifies Coney Island from the contents of Ted's stomach. At the scene of his murder, Esposito shows up with a big plate of food and he splits it with Ryan.
- The Bus Came Back: Castle's father Jackson Hunt makes his return, since the murder victim, Ted, was helping him with a mission to recover a list of deep cover operatives stolen from the CIA.
- Call-Back: Beckett remembers seeing Jackson's face from the sketches that were made while investigating Alexis' kidnapping.
- Chekhov's Gun:
- It's a mystery why Ted was moved from his murder scene to his apartment. Hunt wanted to be able to keep tabs on the case through Castle, and so moved the body to ensure Beckett's team would land the case.
- Ted was murdered so Gemini could get a coin from his shoe, an Iranian Rial.
- Chekhov's Gunman: The homeless man that Castle gave spare change to in the park turns out to have been Gemini keeping tabs on him and Jackson.
- Elopement: While Castle and Beckett are discussing potential wedding dates, Martha suggests that they should just forgo a ceremony and get married at City Hall. They both dismiss the idea out of hand.
- Genre Savvy: Gemini knew to look for any hidden failsafes on Ted's body, such as the Iranian coin hidden in his shoe. Castle (and Jackson) only find out about it because it left an imprint on the corpse.
- I Have to Go Iron My Dog: Castle stutters out an excuse about the cover of his new graphic novel as a cover to go to Central Park and meet with Jackson.
- Internal Reveal: Beckett learns that the prime suspect in her case is also her future father-in-law.
- Jurisdiction Friction: Jackson deliberately moved Ted's body from Coney Island to Ted's apartment (which is in the 12th precinct's territory) to avoid this, and thereby making sure that his son and his detective fiancée would get involved in the ensuing murder investigation.
- O.O.C. Is Serious Business: Beckett becomes concerned about Castle when he doesn't spout a single wild theory about conspiracies or international espionage when they discover the imprint of the Iranian coin on Ted's ankle, presumably because it hit a little too close to home for him since his father, who deals in international espionage, just surprised the hell out of him.
- Rogue Agent: Hunt is going after Gemini, a mole in the CIA who stole the list of undercover agents. The story of Hunt breaking out of prison by killing three people is a cover that lets him move freely through the sorts of people Gemini would sell the list to.
- Spy Fiction: Hunt shows up again, this time hunting a rogue agent. This generates a lot of distrust on both sides as no one knows if Hunt is really rogue of if he's hunting a rogue.
- Take That!: When Castle speculates that maybe Ted's body was moved was a case of Weekend at Bernie's gone wrong...Castle: Wait, no, that would imply there's a Weekend at Bernie's gone right.
- Worst Aid: Hunt shows up to get a bullet removed. They boil the crap out of everything, but they end up having to use an X-Acto knife and a pair of needle-nose pliers with a cut open washcloth covering the wound.
