Food has been mysteriously disappearing from Castle's place lately. Alexis suggests that tiny borrowers have been coming out at night. Castle scoffs at the notion. They'd be way too small to pull open the fridge. Castle vows to solve the case of the missing leftovers, but first he must tackle a more pressing murder mystery. Anne Cardinal succumbs to her ghastly wounds after being dumped in front of a hospital. Her face bears a claw-like wound. It could have come from her job site, as the victim worked an animal sanctuary for primates.
Dr. Paul Devlin was Anne's faculty adviser at Hudson University. None of the animals at his sanctuary have ever shown any aggressive behavior, but Castle fingers a big gorilla named Moonshine as a primate suspect. He believes Rise of the Planet of the Apes was a cautionary tale. The do-gooder ex-con who dumped Anne at the hospital leads the team to the alley where she was killed. Castle believes the footprints they find belong to the killer. They are huge, beast-like impressions. Castle realizes this can only mean one thing. The killer they seek is the legendary Bigfoot.
Beckett is more interested in the other set of smaller, human footprints in the alley. Still, the last phone call the victim made was to the world's foremost authority on Bigfoot, Dr. Darrell Meeks (guest star Raphael Sbarge from Once Upon a Time). The guy says Anne may have had evidence that the legendary beast made his way into the city. She could have been targeted by someone looking to cash in on a TV show's million dollar reward for evidence of Bigfoot. Anne was, indeed, seen arguing with Chase Diggins, an Australian hunter who lost his hand in an alleged Bigfoot attack. The hook he now bears could have left the wound on Anne's face.
Chase Diggins says Anne drew him to the city after she claimed to have found a squatch. His boot print was in the alley where she was making fake Bigfoot prints. Diggins believes Anne was doing this to throw of others because she found the real Sasquatch. In other news, Perlmutter discovers a pendant in the murder victim's stomach. She swallowed it around the time she was attacked. It belonged to her old college roommate, Justine Bolton, who was murdered a year ago.
Justine's boyfriend, Kurt Wilson, was the prime suspect her murder. Anne was looking into the case. Footage from her video camera shows her being attacked in the woods by an unidentifiable figure. Castle still thinks it could be Bigfoot. He makes Sasquatch-like sounds to draw the beast out during a search of the woods where Anne was initially attacked. Castle and Beckett fall into a pit trap in the ground. She's able to climb out to go get a rope. Castle thinks Beckett has returned when he hears noise from above. Unfortunately, it's someone a lot hairier than his partner. Castle has come face-to-face with Bigfoot!
Beckett draws her gun on Bigfoot, who falls backwards into the pit. Castle wants her to shoot the beast until he realizes it's Dr. Darrell Meeks in disguise. He leads them to the spot where Anne was killed. He stumbled across the murder weapon while on his Bigfoot hunt. Back in the city, Ryan and Esposito track down Kurt Wilson. He was living in the woods where Anne was attacked. She was trying to help him because she believed he was innocent of her roommate's murder. Kurt leads Castle and Beckett to the real killer, the serial stalker former professor, Dr. Paul Devlin. Anne knew he was a murderer when she saw him with Justine's pendant. Case closed.
Castle and Beckett have a nice discussion about their beliefs. She's all about everyday magic like nature and John Coltrane. Castle appreciates that which is possible and unknown. Beckett believes in one unexplained phenomenon: the two of them. This sweet declaration is interrupted when Castle's booby trap catches his food thief red-handed. Actually, Alexis is caught blue-faced thanks to a dye pack. She admits she blew her allowance investing in a friend's idea to help clean the air via bamboo forests atop skyscrapers. Castle wants to know more about this wild idea. After all, he's a big fan of that which is possible.