‘Castle’ was one of the last shows I caught up with before the Christmas break, and it also happens to be one of the first back with new episodes in January. Normally, I let this series sit on my DVR for a bit before watching. Due to lack of anything else worthwhile on the air this week, I tuned in early. Boy, am I glad I did. This week’s episode is one of the most entertaining of the show’s entire run.

First let’s get the business of the murder-of-the-week plot out of the way. The victim was one of those “millionaire matchmaker” women like Bravo has Reality shows about. She was thrown out of her apartment window and impaled on a fence below. (Icky!) Despite a downturn in business, she had a suitcase full of cash that had something to do with a honey trap scheme. The killer was either her mark, or the mark’s spouse. I forget which. It’s not important. This storyline is the least interesting thing about the episode, and is hardly even relevant to anything else going on except as a pretense to give the characters a case to investigate.

You’ll notice that the episode title, ‘Nikki Heat’, is of course the name of Castle’s fictional heroine, the one based on Beckett. His first book in the series, ‘Heat Wave’, is being turned into a movie, and he’s not terribly happy about the casting. Nikki will be played in the movie by Natalie Rhodes (Laura Prepon from ‘That ’70s Show’), a scream queen famous for starring in crappy horror flicks with titles like ‘Hell’s Crawlspace’, ‘Knife 2’, and (of course) ‘Knife 3D’. Castle is skeptical that she has the chops to pull off the role. On the other hand, Beckett doesn’t seem at all phased by this. Ryan and Esposito are both psyched.

Castle’s mood especially sours when Rhodes turns up at the police station to shadow Beckett for research into the character. She’s never read Castle’s book, and spends most of her time annoyingly typing into a Blackberry. He pegs her instantly as a Hollywood bimbo. What really gets on his nerves, naturally, is the fact that she’s a bigger celebrity than he is. Everybody falls all over themselves to meet and have pictures taken with her. “It’s not every day we get somebody famous in here,” Beckett blurts out without thinking.

Early scenes are played for a lot of effective comedy as Castle bemoans having his spotlight stolen and his character desecrated. However, around this time, I couldn’t help thinking to myself that just once I’d like one of these shows to bring in a starlet character who’s not just a bimbo. That’s pretty clichéd at this point, isn’t it?

Then a funny thing happens. As the episode goes along, that’s pretty much exactly where it goes. Rhodes turns out to be a more dedicated actress than she initially seemed. She’s approaching the role seriously, and has taken detailed character notes. By the time she puts on an appropriate wig and wardrobe, she pulls off a pretty dead-on Beckett impersonation. So much so that Beckett and the other cops suddenly get weirded out by the uncanny doppelganger.

She even manages to save the day at the end. When the killer threatens to kill himself rather than be arrested, Rhodes steps in with a cheesy line from the movie script about how he should think about his family. She delivers it convincingly enough that he really does think about his family, and puts his gun down.

Castle is finally won over when she reads his book and tells him that she’s going to demand the movie script be revamped to make it more faithful to what he’d written. Also, it doesn’t hurt that she tries to seduce him as “character research.” (He declines, but just barely.)

As all of this is going on, a side story has Ryan on the verge of proposing to his girlfriend. This goes disastrously wrong when she catches him in a lie about where he’d been one night. (He was really visiting her parents to ask for their permission, but he can’t tell her that.) She nearly breaks up with him when she learns that Rhodes has been working in his station, because Rhodes was one of the celebrities on his “Freebie Five” list, and she draws her own conclusions about what he’s been doing. Fortunately, Ryan pulls it all together at the end by telling her the truth and proposing in the police station.

This episode is a huge amount of fun, and Prepon is really entertaining as the “creepy Beckett.” I hope she gets to come back for a ‘Heat Wave’ movie premiere or something.