The story begins in 1825, set in the rugged terrain of northeastern Australia, where a solitary Chinese man is diligently panning for gold alongside a river. Almost instantly, he discovers a sizeable nugget, but his triumph is short-lived as he is violently robbed at gunpoint by an unidentified man who swiftly takes off into the bush. This unnamed robber soon encounters the notorious outlaw Thunderclap Newman, who asserts his claim over the gold nugget. However, their confrontation is abruptly interrupted by the chilling screams of the Chinese man, who meets a grim fate offscreen, followed by terrifying roars that echo through the wilderness. In a bid to escape the imminent danger, Newman shoots the robber in the leg, hoping to distract the encroaching threat. Unfortunately, the beast—a large, hairy, ape-like creature—quickly dispatches the unidentified man and, moments later, catches up with and kills Newman.
Fast forward to the present day, where we meet two treasure hunters, Jack and Kent, who have taken on the roles of exterminators but are keen on unearthing Newman's fabled gold. They paddle up the same river witnessed in the opening scene, determined to find their fortune. After an adventurous day of navigating through the bush and setting camp for the night, the duo wakes up the next day with high hopes, using GPS to lead them to a hidden network of lava tubes. Success follows shortly as they stumble upon Newman's gold. However, trouble arises when Kent, in an unexpected twist of betrayal, attempts to kill Jack. Kent's attention diverts when he notices a movement on the opposite bank of the river. In a bid to preserve his life, Kent abandons Jack and the gold, opting to investigate the mysterious figure instead.
Meanwhile, Rhiannon, the vigilant park ranger, sees the smoke from their campfire and decides to check it out. Upon arrival, she finds Jack, who had merely blacked out following Kent's attack yet somehow possesses the bag of gold. Realizing the danger posed by Kent, Jack hastily hides the gold in the river while urging Rhiannon to call the police for help. However, Kent catches them just as Rhiannon is about to use her radio, taking charge of the situation by holding them at gunpoint. With a menacing order, he demands Rhiannon throw her radio into the river and threatens both their lives unless Jack reveals the location of the hidden gold. Jack cleverly misleads Kent regarding the gold's location and leads him through the dense bushland, where they stumble upon a makeshift sleeping area and an intimidatingly large footprint. Despite dismissing the footprint, Kent's bravado fades when a terrifying roar captures his attention. Seizing the moment, Jack overpowers Kent, snatches his gun, and flees with Rhiannon. Left alone, Kent manages to find temporary shelter in a hollow tree trunk, a tight fit for the chaotic creature that chases after him. In a last-ditch effort to protect himself, he uses a pocketknife to fend off the beast.
As they frantically navigate this perilous situation, Jack and Rhiannon come to the realization that the creature will not cross water, offering them a momentary escape route. Meanwhile, back at the riverbank, Kent finds himself face-to-face with Detective McNab, portrayed by Vernon Wells, who is investigating a series of strange disappearances in the area. McNab is skeptical of Kent's story about being in the remote location, especially upon noticing the bloodied pocketknife in Kent's possession. As he handcuffs Kent to a tree root, McNab brushes off Kent's claims of an "evolutionary throwback ... a yowie." However, while trying to report to the local police, McNab's attention is drawn to the yowie that he now witnesses. Just then, his phone rings while he tries to take a photo of the creature, leading to a horrifying end as the yowie brutally dismembers him. In desperation, Kent breaks his own hand with a rock to escape the handcuffs and continue his pursuit.
In a tense moment of betrayal and confrontation, Jack, while Rhiannon is asleep, tries to recover the gold but finds himself sandwiched between Kent—armed with McNab's gun—and the menacing yowie. Kent, believing the creature has done away with Jack, chases after Rhiannon, shooting her in the leg and taking her hostage in a shocking turn of events. He uses her as bait to ensnare the yowie in a deadly ambush. In a twist of fate, Jack, who has been impaled but not killed by the beast, manages to escape with Rhiannon, who is taken back to the yowie's lair.
During a pivotal moment, Kent confronts Jack, coming to the realization that Jack has hidden the gold in the river. Jack, recognizing the gold as a curse, pleads with Kent to focus on the danger posed by the yowie. Yet, Kent remains driven by greed, leading to a violent struggle between the two. Ultimately, Jack triumphs, leaving Kent behind, and he goes in search of the yowie. Encountering Rhiannon, who is unconscious, and a collection of items stolen from previous victims, Jack musters his strength for one last confrontation. Faced with the overpowering yowie, Jack resolves to escape with Rhiannon. They reach a sheer cliff, the creature hot on their heels. In a moment of bravery, Jack reveals he has pilfered a stick of dynamite from the yowie's stash. He swiftly throws the lit stick at the creature's feet, resulting in a cataclysmic explosion that obliterates the beast.
Finally, navigating their way through chaos and danger, Jack and Rhiannon embark on a trek along a dirt road, striving to return to civilization, leaving behind the horrors of the bush and the hard lesson learned about greed and survival.
