Credit: Karen Neal/ABC Television Group © 2011 Disney Photo: Beckett and Castle in Season 4, Episode 5: “Eye of the Beholder”

Caskett shippers will definitely not want to miss tonight's all-new episode of Castle!

Guest star Kristin Lehman shakes things up as Serena Kaye, a super hot, smart-mouthed art insurance investigator (think Rene Russo in Thomas Crown Affair), who gives Beckett a serious case of the green-eyed monster when she flirts with Castle. As much as we hate seeing Rick crush on other women, we think this is just the wake-up call Beckett needs.

What brings our crime-solving duo to this highfalutin art world, anyway? You guessed it. A murder linked to the theft of a very valuable work of art. Detective Esposito fills them in on the gory details at the crime scene.

So, how did the killer gain access to a swanky art gala? Castle and Beckett start doing that adorable thing they do, but are interrupted by someone who happens to know a teensy weensy bit more about this stuff. Enter: Serena Kaye.

Beckett finally caves and allows Serena to lend her "value assets" to the investigation, although it soon becomes apparent she's kicking herself for that decision. Jealousy isn't an emotion Beckett has much experience with, it seems.

Meanwhile, back at the Castle homestead, Martha notices that her son's social life has been a little — how do we put this mildly? — lame. He may be getting his flirt on with a saucy insurance investigator, but we all know his heart really belongs to his beautiful, brown-eyed muse. Sigh …