Many Castlefans probably cheered last week when, despite their separation, Castle and Beckett celebrated their first wedding anniversary with some time between the sheets. So, is the separation officially over? Not so fast.

Although Monday's midseason finale (10/9c, ABC) keeps those happier vibes going — especially when Beckett (Stana Katic) and Castle (Nathan Fillion) try to solve a murder case together while stuck on a cruise ship — when the case reveals a possible connection to the larger LokSat mystery, Beckett is again reminded why she pushed Castle away in the first place. And things only get tougher between the couple when Castle does some digging of his own and uncovers more of Beckett's deception.

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Elsewhere, the episode introduces Kristoffer Polaha's recurring character. "He plays a public defender," executive producer Terence Paul Winter says. "He's a true believer in justice, which is very similar to Beckett." However, that doesn't mean they won't butt heads. "By design, public defenders are often at odds with the NYPD because they represent a lot of the criminals the 12th precinct brings in," Winter says. "That will create a bit of conflict that will carry on into future episodes we're planning in the new year."

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