Brian Kessler, portrayed by David Duchovny, is a graduate student in psychology and an aspiring journalist whose recent article about serial killers piques the interest of a publisher, leading to a lucrative book deal. However, after depleting his advance, he realizes the urgency of finishing his book. Encouraged by his photographer girlfriend, Carrie Laughlin, played by Michelle Forbes, Brian decides to journey from Pittsburgh to California, stopping at notorious murder sites along the way. To offset their travel costs, he posts a ride-share advertisement.
Meanwhile, we are introduced to Early Grayce, a sociopathic parolee brilliantly portrayed by Brad Pitt, who has just lost his job. His parole officer arrives at his trailer park, where he lives with his young girlfriend, Adele Corners, depicted by Juliette Lewis. Early dismisses the officer's job offer as a college janitor, insisting he wants to flee the state. The officer warns him that failure to keep his appointment will land him back in prison, prompting Early to reluctantly go for the interview. On his way out, he encounters his landlord over unpaid rent, leading to a violent outburst as he drives recklessly around the park.
Noticing Brian's ride-share ad at the college, Early contacts him and they agree to meet the next day. He sends Adele ahead, and unbeknownst to Brian and Carrie, he has already committed murder by eliminating his landlord. Carrie is uneasy upon meeting the rough couple but encourages Brian to give them a chance, albeit begrudgingly.
As the journey unfolds, Early's malevolence becomes increasingly apparent. He kills an unsuspecting man at a gas station and, during a stay at a hotel, even goes so far as to cut Adele's hair to mirror Carrie's style. In a revealing moment, Adele confides in Carrie about her traumatic past, emphasizing how she sees Early as her protector despite his violent history. Concerned for Brian's growing intrigue towards Early, Carrie issues an ultimatum—either they distance themselves from Early and Adele or she will leave.
Their road trip takes a dark turn when Carrie sees a news report highlighting Early as a suspected murderer. The situation escalates as Early kills a gas station attendant and attacks two police officers, ordering Brian to execute one of the wounded. When they arrive at the home of an elderly couple, Early brutally murders the man, although Adele chooses to let the woman escape. The conflict reaches a breaking point when Adele confronts Early, declaring that she wants nothing more to do with him, leading to her tragic death as Early turns his gun on her.
Regaining consciousness after being struck by Early, Brian receives help from the elderly woman who gives him the keys to her truck. In a breathtaking climax, he arrives at an abandoned nuclear testing site, surprising Early and confronting him with a shovel. After rescuing a traumatized Carrie, the struggle escalates until Brian shoots Early in self-defense, finally ending his terror.
The film concludes with Brian and Carrie in a serene California beach house. Carrie, now with a long hairstyle that represents her newfound freedom, informs Brian about a gallery interested in her art. As they plan to celebrate, an emotional moment unfolds when they hear Adele’s voice on Brian’s tape player, reminiscing about the kindness they showed her and Early, highlighting the bittersweet impact of their intertwined fates.
