In February 1969, Hollywood actor Rick Dalton (Leonardo DiCaprio), the former star of the 1950s Western television series Bounty Law, finds himself in despair over his waning career. Over lunch with Producer and Agent Marvin Schwarz (Al Pacino), Dalton comes to a painful realization: accepting guest roles as a villain in new network shows could ultimately tarnish his legacy, leaving him branded as a "has been." His best friend and former stunt double, Cliff Booth (Brad Pitt), who also struggles with whispers of his troubled past—including rumors surrounding his wife's death—drives Dalton around, as he relies on Dalton for work.
Their lives become intertwined with rising actress Sharon Tate (played by Margot Robbie) and her husband, director Roman Polanski (Rafal Zawierucha), who move in next door. Dalton dreams of befriending the couple to rekindle his status as a leading man in the film industry. That evening, Tate and Polanski attend a glamorous party at the Playboy Mansion hosted by Hollywood hairstylist Jay Sebring (Emile Hirsch), a longtime friend and former lover of Tate.
Back at Dalton's house, Booth reminisces about a sparring session he had with martial arts legend Bruce Lee (Mike Moh) on the set of The Green Hornet. Meanwhile, cult leader Charles Manson (Damon Herriman) stops by Tate and Polanski's home in search of record producer Terry Melcher, but is turned away by Sebring. Later, while driving Dalton's car, Booth picks up a hitchhiker known as "Pussycat" (Margaret Qualley) and drops her off at Spahn Ranch— a location with a dark past. While there, "Pussycat" urges Booth to stay, but he feels wary of the many hippies squatting at the ranch, led by the nearly blind George Spahn (Bruce Dern), who has been manipulated by Manson.
Driving away from the ranch, Booth finds trouble when he discovers that Clem Grogan (James Landry Hébert) has slashed his tire. A confrontation ensues where Booth unleashes his fury on Grogan, compelling him to fix the tire. Meanwhile, one of the Manson girls, Sundance (Cassidy Vick Hice), seeks help from Tex Watson (Austin Butler), but by the time he arrives, Booth is already on his way. During this time, Tate decides to walk to a nearby theater to watch her performance in The Wrecking Crew.
Dalton's luck seems to change a bit when he lands a role as a villain in a new series titled Lancer, where he engages in a meaningful exchange with his young co-star, Trudi (Julia Butters). Despite his struggles with alcohol, Dalton manages to deliver a compelling performance that rekindles his lost confidence, impressing director Sam Wanamaker (Nicholas Hammond) and Trudi alike.
Following a notable guest appearance on The F.B.I., Marvin Schwarz (Al Pacino) offers Dalton a chance to film a Spaghetti Western in Italy. Although he views these films as the bottom of the barrel, Dalton accepts the offer, bringing along Booth for the six-month shoot. He ends up filming several movies, including Nebraska Jim with Sergio Corbucci, and even gets married during his time abroad.
When they return to Los Angeles, Dalton finds that he can no longer afford Booth's services, and the two decide to part ways amicably. They share a drink one last time before heading back to Dalton's home, where Booth indulges in an acid-laced cigarette and takes his loyal pit bull, Brandy, for a walk. However, a sinister plot unfolds as Tex Watson, Susan Atkins (Mikey Madison), Linda Kasabian (Maya Hawke), and Patricia Krenwinkel (Madisen Beaty) arrive outside in their loud 1959 Ford Galaxie, following Manson's orders to murder everyone in Tate's house.
Upon hearing the commotion, Dalton steps outside and confronts them, demanding that they leave. Although they drive off momentarily, Atkins devises a plan to return and take Dalton out instead. The trio breaks into Dalton's home, but Booth, recognizing their backs from Spahn Ranch, springs into action, commanding Brandy to attack. A fierce fight ensues, culminating in Booth and Dalton taking down the intruders. In a climactic moment, Dalton retrieves a flamethrower he had kept from a film shoot and uses it against Atkins. After the chaos, Booth is taken to the hospital, and in the aftermath, Sebring has an engaging conversation with Dalton, who receives an invitation from Tate over the intercom to join her and her surviving guests for a drink, rekindling a glimmer of hope amidst the turmoil.
