In 1969 Los Angeles, Rick Dalton (Leonardo DiCaprio) is a popular action star, but after his hit TV show Bounty Law is canceled due to his alcoholism, he feels that his career is in decline. He is given an offer to fly to Rome with his best friend and stuntman Cliff Booth (Brad Pitt) to shoot Spaghetti Westerns, but Rick thinks that this would be a career low for him. When he finds out that his new neighbors are Roman Polanski and Sharon Tate (Margot Robbie), Rick thinks he has a chance at reinvigorating his career.
While Rick is filming an episode of the series Lancer, Cliff meets a young hippie woman and brings her back to her home on Spahn Ranch, where the infamous Manson Family lives. At the same time, Sharon, a fairly new actress, watches her own movie, The Wrecking Crew, in a theater, and she is happy to hear the positive reception from the audience.
Rick and Cliff eventually fly to Rome for the Spaghetti Westerns, and Rick comes back married to an Italian film star named Francesca Capucci. He and Cliff feel that it is time they part ways. This happens on the night of August 8th, 1969. Manson Family members Tex Watson, Sadie (Susan Atkins), Katie (Patricia Krenwinkel), and Flowerchild (Linda Kasabian) show up to kill a pregnant Sharon and her friends, until Rick comes out to yell at them to leave. Sadie then suggests they kill Rick and his friends, but Flowerchild leaves them before they carry out their plan. The three find Cliff, who is high on acid, and he sics his dog on Tex and Sadie before stomping Tex's face in and then smashing Katie's face all across the house. Rick kills Sadie by burning her to death with a flamethrower.
Cliff goes to the hospital for injuries, and Rick ends up meeting Sharon and her friends.