Rick Castle and Kate Beckett are not working as a team in "Castle" Season 6 Episode 17, "The Belly of the Beast." In the episode, Beckett is not on call, but looks like has to cancel her plans with Castle to assist a dangerous Narcotics investigation.
The sneak peek of the episode shows Captain Fowler briefing Beckett about a drug ring on which they don't have much information. He wants Beckett to impersonate one of the women, a low-level drug courier, and infiltrate the drug ring. However, Beckett cannot talk about this undercover operation with anyone else, including Castle. Captain Fowler wants Beckett to go to a meeting in place of the low-level drug courier woman.
Beckett just has to meet the contact and leave in an hour. However, it does not seem to be an hour meeting. The sneak peek provides a glimpse of a man pointing a gun at Beckett in the lift.
In another sneak peek, Beckett can be seen promising Castle that she will be back for dinner. It, however, looks unlikely that she will be back on time for that, as the undercover operation will turn "deadly." The promo of the episode suggests that Beckett will be captured. Also, the synopsis of the episode alludes to a powerful enemy from Beckett's past making an appearance.
Beckett may have not told Castle about her mission, but the man for sure knows how to dig-out information. And when his lady love is in danger, he for sure will do anything to rescue her.
Official Synopsis of "Castle" Episode 17, "The Belly of the Beast,": "Beckett is recruited to assist on a Narcotics investigation, but a routine mission turns deadly when an undercover operation goes array. To survive, Beckett must engage in a battle of wits against some of the most dangerous men in the New York underworld - including a powerful enemy from her past."
Andrew W. Marlowe and David Amann have written "In the Belly of the Beast," while Rob Bowman has directed it.