In Los Angeles, Billy decides to visit Stanley's, a restaurant where Sarah works. After numerous visits, he gathers the courage to ask her out. One fateful night, Billy receives a troubling phone call, prompting him to drive his old early-70s Malibu to a hotel that has seen better days. In a rush, he accidentally knocks on the wrong door, where a man with an angry, notable voice informs him that Sarah is next door. To his shock, he finds that Sarah's roommate Ellen is found dead on the sofa, while Sarah is upset but alive in another part of the room. She reveals to Billy that Ellen has been harmed by a drug dealer. Billy manages to convince Sarah to leave with him, though in the chaos, she mistakenly grabs the wrong bag.
Once settled in a motel, Sarah discovers she has taken a bag filled with Ellen's belongings. Inside, she finds a letter from attorney Cameron Brogden in Tremo, Texas, revealing that Ellen's wealthy uncle, Niles, has passed away and left everything to her. Billy suggests that Sarah should impersonate Ellen to claim her inheritance, especially since the bag conveniently contains Ellen's driver's license.
Upon arriving in Tremo, the couple makes their way to a large, older house, where Billy uncovers a key hidden outside and gains access to Niles' home. They soon meet with Cameron to discuss the inheritance, but he warns them of a potential complication: Niles might have had a son not mentioned in the will. Their investigation leads them to discover the site of Niles' tragic death, where his tractor still lies abandoned.
Meanwhile, Cameron and his brother Bob, the local sheriff, are seen sharing a meal at a diner, revealing a familial connection that has influenced Bob’s position. The couple uncovers a letter from Ellen's uncle asking him to acknowledge the son he had out of wedlock. Despite their discomfort, they are uncertain about staying in the uncle's house where a former housekeeper, Belle, wishes to continue her work.
Tension builds when a man tries to steal an early 70s Ranchero parked nearby. Sarah, mistakenly thinking it’s a threat, grabs a hunting rifle and accidentally fires it, hitting the man as he tries to escape with the vehicle. As the couple scrambles to hide the Ranchero, Bob and deputy Earl arrive to investigate the theft, and they mistakenly call the Ranchero an El Camino. Billy, knowing the cops would require a warrant and aware that they can’t go far without it, works to cover his tracks.
The investigation into Niles' death takes a dark turn when it’s revealed that he was strangled, and law enforcement begins to view Billy as a suspect. While Billy is pushed to submit his fingerprints, Sarah remains unchallenged. As the plot thickens, incriminating evidence surfaces in the form of a DVD suggesting Niles' unconventional sexuality could have implications regarding his heirs.
The situation escalates when drug dealer Eddie confronts Sarah, demanding repayment for Ellen's debts, taking her to a motel and clouding Billy's judgment as he fears she's following in Ellen's dark footsteps. Tension mounts further when Billy confronts Sal, a store owner abusing his son, which leads to a parking lot showdown, leaving Billy injured and cared for by Belle, who turns out to have pivotal familial ties.
After a series of harrowing moments, including a bloody incident involving Sarah disposing of what looks like a body, Billy learns from Sly Wheaton, a dubious lawyer, that Niles intended to cut out the illegitimate son from any fortune. Even as Cameron finds incriminating evidence against Billy and deliberately destroys it, the couple's safety remains in jeopardy.
With the stakes rising, the sheriff uncovers Billy's criminal history, escalating the case against him. The shocking revelation of Eddie's body found in the Cadillac deepens the mystery. Eventually, an analysis of handwriting uncovers an unexpected twist revealing Belle as the illegitimate son’s mother.
Desperation mounts as Billy and Sarah face the truth: their plan has unraveled completely following Sly's shocking death. When Cameron asserts his claim to the inheritance with a gun, their fate hangs in the balance until Bob and Earl intervene, culminating in a tense standoff where Cameron is shot.
In a desperate bid for freedom, the couple flees toward the Mexico border but not without a final confrontation with Eddie. A gripping flashback unveils Eddie's ties to Billy, revealing a calculated revenge scheme. After a fierce struggle, Eddie meets his end, leaving Billy and Sarah to share a passionate kiss amidst the chaos they have endured.
