Along a desolate stretch of desert highway, an old gas station named Fred's Oasis stands in disrepair, where its grumpy owner, Fred, is busy packing up his belongings into a pickup truck. His solitude is interrupted by the sudden appearance of a wild and somewhat disheveled young woman named Ruby, who bluntly states, “we're hungry” while suggesting a trade for goods pilfered from an Air Force PX. Fred warns Ruby to tread carefully, as local investigators are on the case regarding the theft. Sensing Fred's intention to leave, Ruby desperately implores him to take her with him, only to be met with his derisive laughter and harsh words, claiming she would never blend in with “regular folk.” Moreover, Fred ominously mentions that her father, Jupiter, would end her life if he discovered her intentions, to which Ruby boldly replies that Jupiter wouldn’t hesitate to kill Fred either.
Their tense standoff is abruptly interrupted by an external voice that could belong to a state trooper, prompting Ruby to hide in a back room while Fred goes to investigate. Fortunately for him, instead of a trooper, he finds a family in need of fuel: Big Bob Carter, a retired Cleveland police officer whose heart trouble forced him into early retirement; his wife Ethel; and their three adult children, Lynne, Bobby, and Brenda alongside Lynne's husband Doug, and their baby daughter, Katy. The Carters are on a road trip to Los Angeles, but are taking a detour to visit a local silver mine – a surprise for their 25th wedding anniversary.
When asked for directions, Fred steers them away from the mine, warning that it's long exhausted and that the Air Force uses the surrounding area as a gunnery range. Unknown to all, a menacing figure named Mercury, adorned with a feathered headdress, secretly approaches the gas station. As Fred serves the Carters, Doug unwittingly stumbles into the room where Ruby had just hidden, only to find a broken window stained with fresh blood. He overhears Ruby in conversation with Mercury, pleading that “Grandpa Fred is running away.”
After the Carters leave, Fred’s truck unexpectedly explodes, thwarting his escape plans and leading him to exclaim, “There’ll be hell to pay now!” Intent on locating the silver mine, Bob veers off the main road, only to find himself lost and in the middle of an Air Force nuclear testing zone, resulting in a disastrous accident when he crashes their station wagon. Now stranded, the family prays for divine protection before Bob and Doug venture out in search of help. Meanwhile, they remain under the watchful eye of Jupiter's savage clan.
As the family prepares for lunch, chaos ensues when Beauty, one of their German Shepherds, bolts into the hills, prompting Bobby to chase after her. Horrifically, he discovers her disemboweled body and, consumed by terror, he falls and loses consciousness. As night descends, the women attempt to contact help via radio amidst unsettling heavy breathing on the line. Just then, Bobby emerges from the shadows, claiming that he didn’t find Beauty, while they learn that The Beast has escaped its confines. Doug returns empty-handed, adding to the family's distress.
In a turn of events, Bob finally arrives at Fred’s station only to find it abandoned. Suddenly, a gunshot rings out, followed by a scuffle, revealing Fred attempting to take his own life. Bob intervenes, demanding an explanation, and Fred divulges a dark past involving Jupiter, whose monstrous nature led to the ruin of Fred’s family through a series of tragic events.
In a brutal aftermath, Jupiter bursts into the station and kills Fred mercilessly with a crowbar. Poor Bob collapses, left vulnerable to Jupiter's revenge. Meanwhile, Ruby is imprisoned, forced to consume Beauty's remains, losing her appetite when haunted by the sounds of a dog howling, believing it to be Beauty's spirit.
As night settles, Bobby attempts to warn Doug and Lynne against sleeping outside the station wagon. Once again, tension mounts when an explosion is heard in the distance, followed by Bob's cries of pain as he becomes a victim of Jupiter's cruel intentions. In a frenzied rescue attempt, the women encounter overwhelming horror as Jupiter's wicked sons invade their space, leading to a shocking betrayal among the family and gruesome acts of violence that leave them fighting for their lives against Jupiter's deranged clan.
As the story unfolds with cunning traps and desperate escapes, Ruby surprisingly manages to seize the opportunity to aid in saving the children amidst the chaos. Cunning plans are devised, and in a desperate battle for survival, the surviving members of the Carter family confront their darkest fears and their own moral dilemmas as they fight to reclaim their lives and rescue the innocent from a demented fate.
