Nathan Fillion, Stana Katic Nathan Fillion, Stana Katic

Monday's Castle will once again invite out titular mystery writer to put his overactive imagination to work.

In our exclusive sneak peek at Monday's episode (10/9c, ABC) below, Castle (Nathan Fillion) and Beckett (Stana Katic) snoop around their latest crime scene only to find several odd clues. The oddest, of course, are the large animal-like footprints. For Castle, there is only one reasonable explanation: The murderer is Bigfoot!

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Naturally, the always skeptical Beckett will have a hard time being sucked into Castle's crazy theories. Then again, the evidence may be on Castle's side this time. Watch the video below to see how Castle first pieces everything together. Castle airs Mondays at 10/9c on ABC.