Castle gets trapped in an alternate universe where Beckett is a captain and has never met Castle. And the two finally get married.
Tropes that appear in this episode:
- All Just a Dream: Castle is convinced of this at first, until an offhand comment from Alexis about alternate universes leads him to realize what actually happened.
- Alternate Universe: An Incan artifact sends Castle into an alternate universe. In this universe, he's never met Beckett. Because he never met Beckett, several things are different. Castle never wrote the Nikki Heat novels and instead wrote uninspired dreck. Beckett never solved her mother's murder, so she eventually became captain and never softened. Because Castle stopped making money, Martha had to actually work and goes back to Broadway. Alexis moves to LA to live with her mother because Castle has given up. Lanie is pregnant with Esposito's child, but they're not together. Ryan never got married to Jenny due to his increased workload. And Alexis is a goth brunette! Oh, and the break room coffee is as awful as it was in the pilot.
- Alternate Universe Reed Richards Is Awesome: Inverted in general for most of the characters.
- Castle is broke after writing a book that massively flopped and depends on Martha's acting income.
- Beckett becomes the youngest captain in NYPD history but she finds the job boring and unfulfilling. She also never finds out what really happened to her mother.
- Lanie and Esposito's relationship falls apart after she gets pregnant and he gets cold feet about it.
- Ryan and Jenny broke up as his workload doubled after Beckett's promotion and he ended up neglecting their relationship as a result.
- Played straight for Martha, who successfully revived her Broadway acting career to pay the bills when Castle went broke.
- Bad to the Last Drop: Because Castle was never there to buy them an espresso machine, the precinct coffee is as terrible as it used to be.
- Continuity Nod: During the wedding dance, Castle plays “In My Veins” on his phone, since it was the song they chose to get married to.
- Creator's Oddball: An In-Universe example: in the alternate timeline, Castle apparently never met Beckett and turned away from the pulp crime novels that made him famous to write a pretentious Slice of Life novel that catastrophically flopped and ended his career.
- Deadly Deferred Conversation: Castle never does tell alternate Beckett why he killed off Derrick Storm before he takes a bullet meant for her and the artifact takes him back to his universe just as his Beckett wakes him up.
- Death Glare: When Castle refuses to stay put again and tells Beckett "We make a good team, you and I.", Beckett burns him to death in her mind.
- Diegetic Switch: After Castle starts playing "In My Veins" on his phone, it quickly transitions into becoming the background music as the newlyweds have their first dance.
- Foreshadowing: The courier in the beginning is barely able to keep conscious. It makes sense as the time as he's just gotten off a long flight. It's later revealed the water he's drinking was drugged by his driver to retrieve and switch the artifacts.
- Heroic Sacrifice: Zigzagged. Castle takes a fatal bullet meant for the alternate Beckett. However, as he lay dying, the artifact activated and he wakes up back in his universe alive and unharmed a short time after the flashbang knocked him out.
- Maybe Magic, Maybe Mundane: Perhaps it really was the Incan artifact, or perhaps It Was All A Dream...
- At the end of the episode, Beckett arrests the same three killers that Castle encountered while in the alternate universe. Since he had never seen them in the standard Castle universe, that strongly suggests that the trip to the Alternate Universe was real.
- My Own Private "I Do": After their last attempt to hold a big fancy wedding in the Hamptons ended in disaster, Castle and Beckett go back there to finally tie the knot in a private ceremony with only their closest family members in attendance.
- Running Gag: Just like in the pilot, everyone keeps telling Castle to stay put and he never, ever does, to their increasing frustration.
- Shout-Out: The book that Castle wrote in the alternate reality is Finite Laughter, a reference to the David Foster Wallace novel Infinite Jest, including a suspiciously similar cover. Amusingly, Castle's novel is a terribly written flop in contrast to the reputation of Wallace's Doorstopper.
- Telepathy: Castle handwaves his knowledge of alternate Ryan and Esposito's relationships by claiming to have mind-reading powers.
- [Verb] This!: When he punches out Lark, who had said that no one lives a life without regret, while holding the medallion, Castle yells "Regret this!".
