Natalie Rhodes, a horror film actress who has been cast as 'Nikki Heat' in the film adaptation of Heat Wave, has arrived at the precinct to shadow Beckett to prepare for her role. Much to Beckett's amusement Castle, already less than impressed at the casting decision, is soon seething with jealousy both at no longer being the most famous person in the precinct and how everyone falls over themselves to accommodate her. The tables are soon turned, however, when Rhodes reveals herself to be an unexpectedly dedicated and committed actress — and her absorption of Beckett's character begins to make things around the precinct increasingly uncomfortable. Furthermore, Ryan's plans to propose to his girlfriend hit a snag when it's revealed that he nurses a not-so-subtle celebrity crush on Natalie.
Meanwhile, matchmaker Stacey Collins has been found impaled on a wrought iron fence, and over the course of the investigation it soon becomes apparent that several of the matches she was responsible made for less-than-happy couples — and that she went to extremes to make amends.
The Castle episode "Nikki Heat" provides examples of:
- Accidental Murder: Scott Donner apparently wasn't out to kill Stacey when he confronted her, as he was only trying to get the photos of him cheating on his wife. However, she fell in the struggle and wound up impaled.
- Combat Stilettos: Lampshaded; Natalie notes that they must be hard to run in and that she assumes Beckett wears them as a method of asserting authority and power. Beckett doesn't address the first point, but corrects her on the second, remarking that she simply likes wearing them.
- Did I Say That Out Loud: Used word-for-word by Castle following his reaction to seeing Natalie-dressed-as-Beckett and Beckett side-by-side ("Just like I dreamed it!").
- Digging Yourself Deeper/Freudian Slippery Slope/That Came Out Wrong: Ryan gets an extreme case of foot-in-mouth syndrome whenever he's around Natalie, which eventually culminates in him rambling about how she's on his 'freebie five' list of celebrities who he'd sleep with if he had the chance. To her face.
- Actually, it culminates in a fight with his girlfriend Jenny, which he rectifies at the end of the episode by proposing to her.
- Dramatic Drop: Natalie's appearance in full-Beckett getup causes Castle to drop his pencil.
- Dumb Blonde: Natalie seems like one of these at first, but is revealed to have unexpected Hidden Depths.
- Everyone Can See It: Natalie certainly can.
- Feet-First Introduction: Natalie shows up in person getting out of a car in tall heels.
- Grand Romantic Gesture: Ryan's ready to propose to Jenny. Castle tells him it has to be a hot air balloon proposal. Beckett counters that most women want something more intimate, not involving Reggie the Balloon Guy.
- Green-Eyed Monster: Castle is not happy at all the attention Natalie gets when she first arrives. He gradually warms to her however.
- Honey Trap: Stacey used a sleazy private eye and an escort to set these up in order to trap husbands she thought were adulterers, to help their wives get better divorce settlements.
- Hypocritical Humor: Castle when he tries to dissuade Beckett from letting Natalie Rhodes tag along with them on a case:Castle: She's a civilian! I mean, aren't you afraid she's gonna get in the way and mess up the case?
Beckett: You're kidding, right? - I Just Want to Be You/Irritation Is the Sincerest Form of Flattery: Natalie's "character research" leads her to take on more and more of Beckett's personality traits and tics over the course of the episode, eventually culminating in a full Beckett-style makeover. This causes Beckett both great annoyance and a certain amount of identity-crisis consternation.
- Impaled with Extreme Prejudice: How Stacey Collins goes into the night.
- I Need to Go Iron My Dog: Beckett eventually becomes embroiled in a (from her point of view) teeth-grindingly awkward conversation with Natalie about the UST between her and Castle. It gets to the point where Natalie has completely deconstructed the relationship between the two and asked Beckett to give Castle "permission" to sleep with her (for research purposes, obviously) before Beckett, mortified beyond belief, feels the need to flee:Beckett: I need to go. [points at random] Over there. [scurries off].
- It's for a Book: Natalie's justification for attempting to seduce Castle.
- Ironic Echo: The dialogue in Natalie's audition tape. At first Castle thinks it's hacky, but when he, Beckett, and Natalie have to convince Scott Donner not to kill himself, Natalie repeats a lot of it. And it works.
- Lady in a Power Suit: When Natalie appears as "Nikki Heat", she dons a nice business jacket.
- Method Acting: In-Universe. Natalie is rumored to have stayed in an crawl space for a week to prepare for one of her roles. It wasn't true. She stayed there a month. She lied to the press so she wouldn't look obsessive. In fact, her preparation for Nikki Heat goes so far that she starts in dressing and acting like Beckett to the point where she makes a criminal break in an interrogation and stops the episode's main criminal from killing himself while acting as Nikki.
- Mistaken for Cheating: Jenny thinks Ryan slept with Natalie due to his excuse for getting her parents’ blessing falling through.
- ...Or So I Heard: Alexis is apparently a fan of Natalie Rhodes' movies, but whenever Castle gives her the eye after she gushes about them she appends "... if I'd seen it which I haven't."
- Private Detective: Duke Jones is one of these, and a sleazy type at that.
- Shout-Out: To Buffy; the Heat Wave script is apparently written by "Spike Rosenberg''
- Single-Target Sexuality: Castle's refusal of Natalie-as-Beckett seems to imply that he's heading from his previous playboy ways to this regarding Beckett (though his liaisons with his first choice for Nikki Heat in "The Late Shaft" confirms he's not completely there...yet.)
- Spit Take: Beckett sprays her coffee in reaction to Natalie's question "Is Castle gay?"
- Stylistic Suck: The Nikki Heat movie is ... not great.
- Twin Threesome Fantasy: Castle apparently harbours these concerning Beckett... as he unwittingly reveals when Natalie-as-Beckett and Beckett are standing side-by-side.
- UST: Succinctly summed-up by Natalie Rhodes, much to Beckett's mortification.
- Rhodes: I don't get it. He's into you, but you're determined not to give into these feelings that you clearly have for him, so he fantasizes about you through his writing. It's literally verbal masturbation.
