After spending a week in Palo Alto looking for the thing that killed Jessica, Sam and Dean head to Blackwater Ridge and the coordinates their father left in his journal. At the Lost Creek Trail Ranger Station, Ranger Wilkinson mistakes the brothers for friends of Haley Collins, the sister of a boy, Tommy Collins, who went missing while on a camping trip. On a hunch, Sam and Dean visit Haley, and she shows them the last video Tommy sent her via cellphone before he disappeared. She also informs them that she and her younger brother,Ben Collins, have hired a guide and are heading into the hills to find Tommy the next morning.
Sam does some research and finds that people go missing in Blackwater at regular intervals - every 23 years. He also plays Tommy's last video in slow motion, and he and Dean spot an extremely fast moving shadow on a tent wall. They go to visit Shaw, a survivor of an alleged bear attack in 1959, and the old man tells them that it was not a grizzly that attacked his family, but a creature that was smart enough to unlock the cabin door, roared like no man or animal, and moved like lightning. They go back to Blackwater the next morning and arrive just as Haley, Ben, and their guide, Roy, are setting out for Tommy’s campsite. When the group reaches the campsite, they find ripped tents and damaged equipment. Screams for help sound in the distance so they all run to check, but no one is there and when they return to the campsite their packs have been taken.
With the help of their father's journal, Sam and Dean realize that they’re facing a wendigo. They inform the disbelieving group, and Dean draws Anasazi symbols for protection as they make camp for the night. Sam tells Dean he wants to abandon this hunt and search for their father. Dean replies that they have to help others; it is “the family business.” Once again, cries for help can be heard, and Roy ignores Dean’s warnings and runs into the dark with his gun. He doesn't return.
The next day Sam and Dean explain that wendigo means ‘evil that devours.’ They were once human but became something else when forced to eat human flesh to survive. Tommy may still be alive, as wendigo hibernate and like to store live food, so they follow the wendigo's bloody trail. Eventually, Roy’s dead body falls from a tree and the wendigo appears, causing everyone to scatter. Haley and Dean are taken by the wendigo, but Sam and Ben follow a trail of peanut M&M’s that Dean leaves behind. They eventually find Dean, Haley, and Tommy hanging from the ceiling of an abandoned mine, and they cut them loose.
Dean finds two flare guns along with the rest of their stolen supplies, and while Sam leaves with the Collins siblings, Dean tries to draw the wendigo away. The wendigo follows Sam instead, cornering their group; however, Dean appears from behind it and shoots his flare gun into its chest. The wendigo bursts into flame and dies, and they're able to escape and get help. The group fabricates a story to tell the police - they were attacked by a bear. Haley thanks Dean and then leaves with Tommy and Ben in the ambulance. Dean states that he hates camping and informs Sam that they will find their dad. Sam agrees but in the meantime - he’s driving.
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