"I think you feel trapped and you're serious as hell! But right now, I need you to think about the people who love you. And they need you to PUT DOWN THAT GUN!!"
These are the stirring words of Detective Nikki Heat. Okay, they're actually the audition script words of Natalie Rhodes (guest star Laura Prepon), the beautiful actress who will be playing Nikki in the movie. And, according to Castle, the words aren't all that stirring. That's probably because the screenwriter made lots of changes while adapting his novel. Castle's not all that thrilled with Natalie Rhodes either. He doesn't think a woman who was a braless coed in a movie called "Knife 2" should be playing Kate Beckett…er…uh…Nikki Heat.
Fortunately, there's nothing like a murder to take your mind off casting woes. High-end matchmaker Stacy Collins is found skewered by a fence in an alley. Hours earlier, she was at a surprise party thrown by all the happy couples she'd united. Ryan wonders who would want to kill someone who gave couples such joy. That's probably because he's about to propose to his girlfriend. He just isn't sure how to pop the question.
Castle is shocked when Nikki Heat shows up at the crime scene. Yes, the famed actress Natalie Rhodes has been granted permission to shadow Beckett. She wants to get to know the real Detective Heat. As Natalie researches her role, the team learns that the victim's ex, Brad Williams, argued with her before she was killed. Natalie is impressed with Beckett's interrogation tactics while questioning Brad. She's less impressed with Castle, who is horrified to hear that she never even read his book.
Brad alibis out, but points the team toward a slimy P.I. named Duke Jones and his assistant Chloe. The victim had been making weekly payments of $5,000 to Duke for months to do background checks. Apparently, things didn't work out for one of Stacy's past matchmaking clients.
The mystery thickens when Beckett finds a hidden bag in Stacy's place with 250 grand in cash. Natalie suggests they trace the designer bag ID info which leads them to Tonya Wellington, one of Stacy's clients. Her husband, Bill Wellington cheated on her. An infidelity clause in their prenup means Bill must pay Tonya $100 million. The woman he had an affair with is Duke Jones's assistant, Chloe, who also goes by the name Greta Morgan. She was part of a honey-trap scheme.
As the pieces of the case continue to fall into place, Beckett seems to become more and more unhinged. Why? Well, Natalie is a method actress. In order to become Nikki Heat, she must first become Kate Beckett. That means acting like her, talking like her, dressing like her and, yes, even looking like her. There's only one thing she needs to do to complete her research. She must experience the passion Nikki Heat has with her leading man, who the author based on himself. Guess that's why Natalie and Castle are caught kissing in the elevator...by Beckett.
As you may have guessed, Beckett is a little peeved at Castle the next morning. Ryan's girlfriend, Jenny, is also upset. She thinks Ryan was with Natalie the night before. Actually, he was just hiding the fact that he was asking Jenny's parents for permission to marry her. Beckett's anger subsides after Natalie tells her that Castle turned her down. For him, it would have been way too meta.
As far as the case, the team finds out that Greta Morgan has been honey-trapping other clients with Stacy, who felt bad that she hooked up women with unscrupulous men who planned to leave them penniless. Greta doesn't want to give Beckett the names of the other clients. But she will give them up to Nikki Heat.
One of the cheating men, Scott Donner, accidentally killed Stacy while trying to get back incriminating photos. A desperate Donner points a gun to his head. Beckett's promise of a fair trial doesn't fly. Then Natalie chimes in with these stirring words: "I think you feel trapped and you're serious as hell! But right now, you need to think about the people who love you. And they need you to PUT DOWN THAT GUN!!" He does just that. Castle says, "Guess that script wasn't so hacky after all."
The case is closed and Natalie leaves the team, even though she didn't do all the research she'd hoped to do with her character's creator. As for Ryan, he makes amends with Jenny and finally finds the perfect way to pop the question. He asks her to marry him smack dab in the middle of the squad room. The answer is yes and the applause from his friends echo throughout the entire precinct. Love it!