Credit: ABC Photo: STILL: Kate Beckett Looks Upset in Castle Season 5, Episode 10: "Significant Others"

Castle and Beckett have been blissfully happy throughout Season 5, but all of that might change during Monday’s episode.

In Castle Season 5, Episode 10, “Significant Others,” Rick’s ex-wife, Meredith, waltzes into his loft unannounced, coming to take care of their daughter, Alexis. This is an issue in it of itself, but things get even worse when Kate comes to stay, too! While her apartment is being fumigated, she expects a romantic stay with her beau, but instead is met with an awkward family reunion.

We’ve seen the promo, a slew of spoiler photos, and even a clip of Castle and Meredith’s interaction, but one piece of the puzzle is still missing: Beckett’s reaction.

Surprisingly, the strong-willed detective airs on the side of caution, not saying a peep about the uncomfortable situation to her man. However, Kate does reveal her true feelings to Lanie, and is met with a surprising confrontation: the medical examiner thinks Castle could cheat on her.

“This is Meredith we’re talking about!” Lanie exclaims in the video below. “The deep-fried Twinkie that Castle has ex sex with whenever she rolls into town!”

To see the rest of the heated conversation — including Kate defending Rick — check out the sneak peek video, and then you tell us: Should Kate be worried about Rick cheating on her?

Source: TV Guide