Stana Katic, Nathan Fillion Stana Katic, Nathan Fillion

Things are slowly getting back to normal on Castle.

After dedicating much of Season 7's first two episodes to the investigation surrounding the (still mostly unsolved) disappearance of Castle (Nathan Fillion) on his wedding day, Monday's episode (10/9c, ABC) is going back to basics: Castle helps Beckett (Stana Katic) solve a strange murder by offering up outlandish theories.

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But based on the exclusive sneak peek from the episode below, Castle's latest theory might not be so outlandish after all. When Castle and Beckett investigate the death of a pool shark, all evidence points to a killer with supernatural abilities — aka The Invisible Man. When the duo follows up on their only lead, they each seem to have their very own up close and personal encounter."The Invisible Man is real!" Castle squeals with a mixture of fear and delight in the clip below. And this time, it's hard for Beckett to argue. But has the killer made off with Castle and Beckett's only clue after the attack? Click play below to find out. Castle airs Mondays at 10/9c on ABC.