Beckett learns first hand this week on "Castle" that going undercover is a bit trickier when you're married to a celebrity. The police captain partners with private investigator Hayley to go undercover at a high-end spa in search of a woman with a tattoo on her butt, but her recognizable face will make things difficult.

When Beckett (Stana Katic) and Hayley (Toks Olagundoye) slip into the steam room, one of the other women in the room calls her out as a Castle's wife and a cop. Her friend tells Beckett to call their lawyers, but when Hayley mentions the ink on the bum, their third friend takes off.

The suspect doesn't get far before Beckett catches up and rips the towel off the woman to reveal a dragon fly tramp stamp. Busted!

Watch the sneak peek video below:

Before their cover is blown, Beckett and Hayley try to hide their true identities by talking about Beckett's marriage. Although it's just a cover story, Kate's confession that she wants more "edge" in her marriage may be more telling about her real relationship with Castle (Nathan Fillion), which is currently on the rocks.

Watch the new "Castle" on Monday at 10 p.m. on ABC.