In a small town in the western United States, Sheriff Franklin Hunt (Kurt Russell) shot a suspicious homeless man at night, and then he invited the town doctor Samantha (Lili Simmons) to treat the suspect. In the dead of night, a groom was brutally killed by a mysterious invader, and the suspect and Samantha disappeared. Franklin felt the seriousness of the situation. He summoned Samantha's husband Arthur O. Dwyer (Patrick Wilson) and other villagers to a meeting in the local tavern, and then learned that what happened last night might be the work of a mysterious caveman. This group of barbarians married their relatives and even ate humans, including their biological mothers. Although it was extremely dangerous, Franklin and other warriors were determined to brave the caveman's lair and rescue the kidnapped villagers. This journey was dangerous...