The film opens with a young man, Oliver Quick (Barry Keoghan) talking to someone offscreen about his relationship with Felix Catton (Jacob Elordi). Oliver states that while he did love Felix, he claims he was not in love with him.
In 2006, Oliver attends Oxford University under a scholarship, so he doesn’t fit in with the rest of the students who come from wealth. He is first approached by another student, Michael Gavey (Ewan Mitchell), who is a bit awkward and off-putting, and he also gets off on the wrong foot with another student, Farleigh Start (Archie Madekewe). While returning to his room, he finds Felix with his bike after getting a flat tire. Oliver offers Felix his bike so he can get to his destination, for which Felix is thankful.
Oliver begins to spend more time with Felix, who has taken a liking to him. Oliver effectively starts to ignore Michael, who tells him that Felix and his friends will get bored of him eventually. At one point, Felix’s girlfriend Annabel (Sadie Soverall) hooks up with Oliver after Felix bailed on plans with her, despite her also being one who previously looked down upon Oliver for his supposed poverty. Sure enough, after a while, Felix finds himself rather put off by Oliver obsessively trying to spend time with him.
Oliver later goes to Felix’s room crying, saying he just learned his father passed away, presumably from a night of drinking. Oliver says he cannot go home, as his mother is a drug addict and he doesn’t feel safe in his own home. Felix offers Oliver a chance to join him at his family’s estate in Saltburn over the summer.
After the boys finish their final exams, Oliver joins Felix on the trip to Saltburn and arrives at their sprawling mansion. Oliver meets Felix’s parents, Sir James (Richard E. Grant) and Lady Elspeth (Rosamund Pike), plus Felix’s sister Venetia (Alison Oliver) and Elspeth’s friend Pamela (Carey Mulligan). Elspeth asks Oliver invasive questions about his family and home life, which embarrasses Felix, who has told his family everything about Oliver. Farleigh also stays at Saltburn, since he and Felix are cousins.
Oliver starts to spend time with Felix, Venetia, and Farleigh, first by lounging naked in the field outside the mansion. Later in the day, Oliver watches as Felix masturbates in the bathtub, and then later goes to slurp up the remaining bath water when he is gone.
While he grows closer to Felix, Oliver also starts to hang around Elspeth and Venetia. He first suggests to Elspeth that Pamela is involved in something shady against her as a means to get her away from Saltburn. Later at night, he finds Venetia by the garden and performs oral sex on her while she is on her period. Farleigh witnesses this and tells Felix about it, who expresses discomfort with Oliver being with his sister that way.
The Cattons then host a party at the mansion. During a round of karaoke, Farleigh taunts Oliver by having him go up and sing Pet Shop Boys’ “Rent” to mock him over how he’s basically moved into the Cattons’ home. At night, Oliver goes into Farleigh’s room to threaten him while crawling over him, while also giving him a handjob. In the morning, Farleigh is sent out of Saltburn after it was said that he was attempting to steal from the mansion. Later, while Oliver is with Felix and Elspeth, she casually mentions that Pamela has died, strongly implied to be because of suicide.
With the summer nearly over, the Cattons plan a party for Oliver’s upcoming birthday. Felix then surprises Oliver with a trip to see his mother, which Oliver seems to be trying to avoid. When the boys arrive at the house, Felix is stunned to see that not only is Oliver’s mother Paula (Dorothy Atkinson) healthy and friendly, but his father Jeff (Shaun Dooley) is also alive, and the family is fairly well off. Felix is officially put off by Oliver and his lies, despite him attempting to defend himself. Felix tells him to leave Saltburn after the party.
During the party, Farleigh shows up and mocks Oliver, saying that he has less of a place there at Saltburn than Farleigh does. When the party sings for Oliver, the guests don’t even know his name, leaving him upset. Oliver then goes into the family’s maze outside the mansion, where he finds Felix. Oliver attempts to save their friendship, but Felix is done with him.
In the morning, Oliver overhears people frantically calling out for Felix. The family finds him dead in the middle of the maze where he and Oliver had been arguing. Fairleigh and Venetia collapse to the ground in horror. Oliver later sits down for an uncomfortable lunch with the family, plus Farleigh. Farleigh is accused of having taken drugs the night before that may have contributed to Felix’s death.
fter Felix’s funeral, Elspeth asks Oliver to continue staying at Saltburn. Oliver goes into the bathroom while Venetia is bathing, and she begins to accuse him of preying on her family, as he seemed to be obsessed with Felix despite knowing him for barely six months. The next day, Venetia is also found dead, having slit her wrists in the tub. After her funeral, James demands that Oliver leave Saltburn and even offers to pay him off to leave.
Over a decade passes, with Oliver long having left Saltburn. He reads in a newspaper that James has died. He then runs into Elspeth at a coffee shop, where she is happy to see him. After they catch up, she invites him to go back to Saltburn.
The film then reveals that Oliver has been talking to Elspeth, who is on her deathbed. He then confesses as she lays dying that he was responsible for everything that has happened to her family. Oliver punctured Felix’s bike tire in an effort to meet him and enter his life. He poisoned Felix in the maze after giving him a bottle he drank from, but Oliver had vomited the poison out. He also slipped razor blades next to Venetia to give her the idea to commit suicide. Oliver had also sent an email to get Farleigh removed from Saltburn, and later managed to get Elspeth to sign over all her assets to Oliver, effectively allowing him to inherit all of Saltburn. Oliver once again talks about how he loved and hated Felix, but was never in love with him. He then pulls out Elspeth’s breathing tube to kill her.
Oliver moves into the Cattons’ mansion and later dances around the house naked to “Murder on the Dancefloor”.