Giant footprints at the scene lead Castle to believe Bigfoot is the culprit.

In the Castle episode (Season 5, Episode 20), "paper" likely refers to the missing pages from a researcher's notebook or the scraps of evidence used to track the "Bigfoot" killer. 🧩 The Paper Evidence

The episode centers on the murder of Anne Cardinal, a Bigfoot researcher. Key paper-related elements in the investigation include:

Her notebook contains details about her sightings and the locations she was monitoring in the woods.

gets caught with a face full of blue dye after she sneaks in to take food. Castle Season 5 Episode 20 Recap: The Fast and the Furriest

While Beckett investigates the murder, Castle is busy dealing with his own mystery: someone is stealing his leftovers.

The killer is Professor Devlin , who murdered Anne to cover up the fact that he had harassed and killed her roommate years earlier. 🍳 Bonus Subplot: The "Fridge Ghost"