‘Castle’ Season 8 SPOILERS: Beckett And Hayley Take A Spa Day – Undercover Mission?

Beckett and Hayley are becoming fast friends, enjoying a day at the spa in the upcoming "Castle" episode, "The Last Seduction." But the two women may have an ulterior motive for their day of relaxation.

The Nov. 14 episode will find Castle and Beckett hunting down the murderer of a grifting seducer that takes them into the world of New York's elite. Meanwhile, Castle plans to surprise Beckett on the first wedding anniversary despite their separation.

So what's the reason for the spa trip?

"Castle" co-showrunner Alexi Hawley teased "a bit of an undercover situation" for an upcoming episode (although didn't specify when), according to Entertainment Weekly. He also wouldn't say whether the operation involved Castle or Beckett, but if it is Beckett and Hayley, it won't be their last mission together.

"We think it's really fun to see that stuff going on, so you'll definitely see that from time to time," Hawley told EW.

While the ladies enjoy their girls' day out, Castle will be investigating with Ryan and Esposito. Check out all the photos from "The Last Seduction" in the slideshow above, including Castle's attempts at a worthy surprise for Beckett.

"Castle" returns with new episodes on Monday, Nov. 7 with guest star Adam Baldwin at 10 p.m. on ABC.