Castle is still miserable about Beckett's temporary leave of the precinct for her own personal reasons, and his misery increases tenfold when Ethan Slaughter enters Castle's PI office. Ethan's favourite informant has been killed, and his fingerprints are on the murder weapon. He and a reluctant Castle investigate what happened to his informant, and how it ties into a high-price theft.
Tropes
- Arrested for Heroism: Louis is still going to be sent to jail. Despite his help to the police, he did still steal a multi-million dollar computer chip.
- Awesomeness by Analysis: Louis was able to determine Slaughter's location and hack into his computer to contact him from just a few hints.
- Blatant Lies: After Castle takes off in their cruiser, Ryan and Esposito claim that their car broke down when they request a ride back to the precinct. Given the whispering when they return, it's clear not everyone believes them, but they'd rather have that than admit to Beckett that her husband carjacked them.
- The Bus Came Back: After 4 seasons, Detective Ethan Slaughter makes his return.
- Call-Back: There are several to the XY/ XX episodes.
- Beckett's separation from Castle is part of why she doesn't appear in this episode.
- Castle still has a gun in a hidden compartment in his desk.
- Hayley reappears, and now appears to be a trusted member of Richard Castle Investigations.
- Confusion Fu: Castle and Slaughter's singing confuses the thugs for long enough for them to get the drop on them.
- Cowboy Cop: Slaughter, and to some extent, Castle as well.
- Curb-Stomp Battle: Castle gets his ass kicked again, since he's a novelist and not a trained police officer.
- Faking and Entering: A variant. The killer convinced Victor to carry out his heist of the tower which would serve to cover up his own theft of banking codes in the same building on the same night.
- Hidden Depths: Slaughter shows a lighter side, revealing his intense love for musical theatre and cooking.
- Out of Focus: Beckett is stated to be at a conference out of town, explaining her absence from this episode.
- Scheherezade Gambit: Subverted; it seems that Castle is trying to do this, but he's actually hinting at Slaughter when to start beating the bad guys up after their guard is down from the singing.
- Self-Serving Memory: Played for Laughs by Slaughter. He seems to remember the first time they teamed up as some kind of buddy-cop movie, and gloss over the fact that he nearly got Castle killed 6 times. He made it up because he knew Castle would be more likely to help Ethan again if he posed their previous encounter as a comedic adventure. Also, Ethan has lots of enemies and almost no friends. He considers Castle a friend.
- Spotting the Thread: The killer closing a door wedged open by Victor was what alerted him to the other thief's presence in the building.
- Sympathetic Inspector Antagonist: Ryan and Esposito, when chasing after Slaughter. They're convinced late in the episode that Slaughter is innocent, and then join Castle.
- Teen Genius: Louis is a teenager with an IQ of 190 who invented a device with the ability to crack any electronic lock.
