In late 2006, Oliver Quick, a scholarship student at the University of Oxford, struggles to acclimatize to the upper-class environment due to his lack of experience with their customs. He finds an understanding friend in Felix Catton, a wealthy and charismatic student who empathizes with Oliver's troubled background marked by his parents’ struggles with substance abuse and mental health. After the sudden death of Oliver’s father leaves him heartbroken, Felix offers him solace by inviting him to spend the summer at his family’s grand estate, Saltburn.
At Saltburn, Oliver meets the quirky members of Felix's family, including his parents Sir James Catton and Lady Elspeth Catton, his sister Venetia, and Elspeth's friend Pamela. He also encounters Felix's American cousin Farleigh, with whom he has a prickly past as classmates. As the summer unfolds, Oliver ingratiates himself with Felix’s family, except for Farleigh, and begins to develop an unhealthy obsession with Felix.
In a shocking turn of events, one night Oliver spies on Felix in the bath and indulges in a disturbing act. His behavior spirals further as he initiates sexual advances towards Farleigh, leading to tension among the group. When Felix confronts Oliver about the accusations regarding their activities, Oliver vehemently denies them. The following day, Sir James finds out about Farleigh’s intention to sell some of his valuables, resulting in Farleigh being expelled from Saltburn.
As summer draws to a close, preparations for Oliver's birthday party are underway. To his dismay, Felix reveals plans to reconnect Oliver with his estranged mother, prompting a panic in Oliver. Upon arriving at his family home in Prescot, Felix discovers the truth about Oliver’s deception—his father is alive, and his parents lead a stable life devoid of abuse. Hurt and betrayed, Felix decides against making Oliver’s truths public but tells him to leave after the party. In a desperate attempt to reconcile, Oliver professes his deep feelings for Felix, only to be met with rejection. Felix urges Oliver to seek help.
Tragedy strikes when Felix is found dead in the hedge maze at Saltburn. Oliver insinuates that Felix’s death is linked to Farleigh’s drug involvement at the party, leading James to cut ties with Farleigh. In his solitude, Oliver mourns Felix and pays a haunting visit to his grave, expressing his grief in a disturbing manner.
Following Felix's funeral, Lady Elspeth insists that Oliver remain at Saltburn, creating discord as Venetia accuses Oliver of being the architect of her family’s ruin, labeling him harshly. Despite his attempts to mend fences, Venetia ultimately takes her own life in a bathtub. Troubled by the escalating chaos and Elspeth's attachment to Oliver, James resorts to bribery to ensure Oliver’s departure, which he reluctantly accepts.
Fast forward to 2022, Oliver reads about James’s passing and unexpectedly reunites with Elspeth at a café. Overjoyed, Elspeth encourages him to return with her to Saltburn. As Elspeth falls ill, Oliver reveals his role in orchestrating the tragic unraveling of events at Saltburn. He confesses to having meticulously designed his encounters with both Felix and Elspeth, after which she entrusts all her possessions, including the estate, to him. In a chilling conclusion, Oliver takes his final step by removing Elspeth's life support, claiming Saltburn and the Catton family fortune for himself, and reveling in his newfound freedom by dancing unabashedly in the mansion.
