Two older boys are playing video games out in the woods at their campsite while another one sends a video message to someone named Haley. One of the kids goes out to take a nature call and is attacked. The other two hear and go to check it out – another one gets killed as animal noises fill the air. The last one has only a momentary respite before he's attacked as well.
Palo Alto, California
Sam is visiting his dead girlfriend Jessica's grave when a hand reaches out of the dirt…but it's just a nightmare. They're outside of Grand Junction at Lost Creek, Colorado looking for the thing that killed Jessica, by finding their dad. There's nothing on the map coordinates and they notice there are grizzly bears in the woods. Claiming to be environmental study majors, a local ranger figures they're friends of the "Haley girl." The Haley girl was looking for her missing brother but the ranger isn't concerned. Dean smooth-talks the Ranger into getting the girl's location. They talk to Haley claiming to be park rangers and she expresses her concern, and shows them the last video message her brother sent. Haley reveals she hired a guide and is heading out to find her brother Tommy.
Sam checks the files and finds there have been a number of disappearances every 23 years, supposedly by grizzly bears. Sam checked the video message and spots a super-swift shadow-outline in the background. They track down one survivor, Shaw, who reveals he saw nothing but only heard its roar. It broke into their cabin and left Shaw with a huge scar on his shoulder. Sam concludes it's some kind of corporeal creature, perhaps a "skinwalker" or "black dog." The guys catch up to Haley, her younger brother, and their guide Roy, and convince them they're going along. In a cave, the boys from the campsite are tied up and a horrendous creature approaches to feed off of one of them.
Roy shows off his expertise (and Dean's lack) by spotting and triggering a bear trap. Dean gives Haley the true story about how they're looking for they're father and Haley grudgingly lets them continue with her. Deeper in the woods they spot the devastated campsite and Dean concludes it isn't any of the creatures they thought. They hear a scream and follow the cry into the woods, but realize they've been distracted – when they come back their backpacks are stolen, including Roy's GPS and satellite phone. Sam confronts Dean and checks their dad's journal – there's a picture of a Wendigo, a spirit creature that guns are useless against and that can imitate human voices. Sam tries to warn them to get them to leave, but Roy isn't buying it and Haley refuses to leave without Tommy. With night coming, they decide to settle in at a defensible position.
They make a camp and Dean scribes Anasazi symbols that the Wendigo supposedly can't step over. Sam has been getting irritable and when Dean confronts him, Sam notes that their dad isn't here and never was, and he wants to stop wasting time and go find him. Dean suspects their dad wants them to go into the family business and is leading them into it. Dean figures they should try to help other families. They hear a cry for help from the woods before it is cut off, but figure it's the Wendigo again. Roy apparently shoots it and goes off into the woods, and Dean and Sam follow. Roy is lifted up into the trees.
Come morning, they go over the legend of a Wendigo, and how a man turns cannibal and then becomes such a creature. They note that the Wendigo keeps its victims alive and stores them so it can feed during the winter. The only way to kill it is with fire so they rig up some Molotov cocktails and follow its clawprints before realizing it's leading them on again. Blood drips on Haley from above as Roy's corpse drops down on them. They run and get separated, and Dean and Haley get grabbed by the Wendigo.
Sam and Haley's brother, Gary, continue to look and Gary finds a trail of Dean's M&Ms. The trail leads to an old mine shaft with a posted warning of toxic materials. Entering, they see the Wendigo leave and then plunge through some rotting wood into a lower level and find a strung-up Haley and Dean. They free them and find Tommy's body… but he's not quite dead yet. They free him and find some flare guns in a bag, then head for the exit when they hear the Wendigo. Sam gets the others out while Dean lures the creature away. Sam gets the others running to the exit and then goes back to help Dean but runs into the Wendigo. He gets off a shot that misses then catches up to the others as the Wendigo closes in on them. They get to a dead-end but as the creature closes in Dean nails it with a direct hit, incinerating it. Afterward they pass on the grizzly story as Tommy gets hauled away, and Haley thanks them for their help and wishes them luck finding their father. Dean gives Sam some assurance, and Sam basically acknowledges they're going to be monster-hunting and people-helping.