Castle (2009): Season 5, Episode 20

5 - 20: The Fast and the Furriest

When Castle and Beckett find giant footprints at the site of a vicious murder, the team is forced to confront the unlikely theory that Bigfoot is the killer. But as they trek into the world of primate research, big game hunting and mythological creatures, they realize that finding the man responsible may put them on the endangered species list.