In the backdrop of February 1969, amidst the glitz and glamour of Hollywood, a time of transformation is nigh for former star Rick Dalton, portrayed by the illustrious Leonardo DiCaprio. Dalton, once a household name due to his lead role in the popular 1950s Western series , is now grappling with the stark realities of a career on the decline. This despondency finds a sympathetic ear in Cliff Booth, Dalton's steadfast friend and erstwhile stunt double, played by Brad Pitt. As Dalton navigates the harsh waters of a fading career, he is shadowed by the consequences of his own choices, such as getting canceled in pursuit of film stardom and losing his driving license due to numerous infractions, thus necessitating Booth’s constant companionship as chauffeur.

At a critical juncture, Dalton has a revelatory lunch with Marvin Schwarz, enacted by the venerable Al Pacino, a producer and agent whose insight shakes Dalton to his core. Schwarz highlights the detrimental cycle Dalton is trapped in—accepting villainous guest roles on new shows, which, unbeknownst to Dalton, lead the audience to link the esteemed protagonist to the defeated antagonist roles, thus accelerating his descent from leading man to washed-up actor. In Schwartz’s opinion, an avenue of escape lies in the burgeoning market of Italian Westerns, although to Dalton, this proposition is a disagreeable step down the ladder of cinematic prestige.

Dalton, fully aware of his burgeoning "has-been" status, finds it appalling to consider Italian cinema, further complicating Booth's reliance on him for employment. Booth's livelihood suffers owing to persistent rumors of him having murdered his wife, a stigma that no reputable producer wishes to engage with, despite Booth’s undeniable talent and history as a war veteran settled with his loyal pit bull, Brandy, in a humble trailer. As Dalton contemplates his precarious position, he eyes his new neighbors with envious hope; Sharon Tate, an effervescent portrayal by Margot Robbie, and her talented director husband, Roman Polanski, offer a tantalizing vision of networking redemption.

Sharon, alongside Polanski, mingles in the luminescence of Hollywood’s high society, which Dalton imagines as his conduit back to stardom. The couple’s outings, like an extravagant party at the Playboy Mansion teeming with celebrities, stir dreams in Dalton of a friendship with the movers and shakers that could resurrect his stature in the film industry. Yet, these dreams remain just that—dreams that appear distant as the couple revels in the social circles Dalton yearns to penetrate.

An intriguing subplot unfurls through Booth's anecdotes, offering a glimpse into his brawling past, such as the time he squared off against Bruce Lee on the set of . This altercation, sparked by Lee's audacious claim of defeating Cassius Clay, subsequently leads to Booth earning Lee’s respect, although it further solidifies his controversial reputation. Such a background adds depth to Booth's character and the aura that causes friction on new film sets.

Booth's suspicions are confirmed when he crosses paths with the notorious Charles Manson at the Polanski residence. Manson's ominous presence, combined with his intrusion at the Spahn Ranch—a place familiar to Booth from his days yet now a stronghold for Manson's followers—augments a sense of pervasive darkness. Despite Squeaky's objections, Booth demands to verify George Spahn’s well-being, demonstrating his loyalty and moral compass amidst the eerie composition at the ranch.

Concurrently, Dalton gains a marginal revival of his career through a role in the series , where his struggle to master his lines reveals both his vulnerabilities and fomenting alcoholism. In a triumphant comeback, with Director Sam Wanamaker and co-star Trudi—an absorption by Julia Butters—bearing witness, Dalton overcomes these setbacks, delivering a powerful performance that momentarily infuses him with newfound vigor.

Subsequently, Marvin Schwarz extends Dalton an opportunity that, although initially met with disdain—Spaghetti Westerns perceived as inferior cinema—Dalton obliges, embarking, alongside Booth, on a stint in Italy. This endeavor results in Dalton starring in films such as and marrying Francesca Capucci, an Italian starlet. Upon his Los Angeles return, Dalton’s financial constraints compel him to rename his professional relationship with Booth, symbolizing a poignant end to their symbiotic partnership.

The climax approaches as Dalton and Booth, now on diverging paths but bound by camaraderie, spend a night out, culminating in Booth's experience of an acid-altered reality. Meanwhile, Tex Watson and his crew, under Manson's ominous directive to attack the Polanski home, inadvertently stumble upon Dalton's abode. Ratcheting tension ensues as Dalton's righteous anger repels the initial threat; however, determined to wreak havoc, the cult members return, targeting Dalton.

The ultimate clash epitomizes Booth’s combat prowess as he dispatches the intruders, Brandy figuring centrally in the defense, while Dalton spectacularly eliminates the final threat with a flamethrower—an artifact from . As Booth is whisked away to the hospital, the surviving inhabitants finally converge, paving a hopeful lens for Dalton's turbulent journey as he is warmly invited into Tate’s sphere—a symbolic nod to recognition and redemption within the Hollywood tapestry.