On the 4th of July, Ava Brucks returns to her small hometown of Southport, North Carolina, to attend her friend Danica Richards's engagement party. The celebration marks a joyful occasion, but the day takes a dark turn when Ava, Danica, her ex-boyfriend Milo Griffin, and Danica's fiancé Teddy Spencer decide to drive out to a scenic cliffside to watch the fireworks. During the drive, they invite their former friend Stevie Ward, who had recently completed drug rehab, to join them.
While parked in their vehicle on the winding road along the cliff, a tragic incident occurs. Teddy, in a moment of reckless distraction, causes [Sam Cooper]’s car to swerve off the edge of the cliff, plunging into the darkness below. Even though Ava urges the group to contact the authorities and report the crash, Teddy insists on secrecy. He enlists the help of his politician father, Grant Spencer, to cover up the accident, which sets off a chain of events that will have repercussions for years to come.
A year later, the community is still grappling with the lingering shadows of that night. Ava returns once again to Southport for Danica's upcoming wedding to her new fiancé, Wyatt. During this visit, she reconnects with old friends, including [Milo] and [Stevie], and also meets a new character, Tyler Trevino, a true crime podcaster who is in the town to research the notorious killing spree conducted by fisherman [Ben Willis] in 1997. The gathering quickly turns tense when Danica receives a threatening note reading, "I know what you did last summer," making everyone suspect that the past wasn't buried as deeply as they hoped.
Suspicion quickly shifts toward Teddy, whom the group confronts, demanding answers. Teddy, however, vehemently denies any involvement in the mysterious threats or recent murders. That very night, tragedy strikes again when Wyatt is brutally hacked to death by a fisherman wielding a hook—an apparent resurgence of the killer from 1997, now haunting the town once more. The horrifying sight of the fisherman, who bears a striking resemblance to the late Ben Willis, raises fears that the town’s buried secrets are resurfacing and that someone is targeting those connected to the past.
As the group tries to piece together what’s happening, they realize that someone has intimate knowledge of the old murders and may be coming after them. [Tyler] shows Ava the place where [Elsa Shivers] was murdered by Ben back in 1997, but during their investigation, the Fisherman ambushes them and kills Tyler. Ava manages to escape with a wound but is left shaken. Unable to convince the police or the town to take the danger seriously, the survivors seek help from the former victim Julie James, who suggests that the killer may have a personal connection to Sam Cooper.
Evolving suspicion points toward the town’s pastor, Judah Gillespie, especially after Ava, Milo, and Stevie discover that the car belonging to Sam Cooper is connected to him. Meanwhile, Danica and Teddy visit the local cemetery and recognize graves belonging to some of the original victims—[Helen Shivers], [Elsa Shivers], and others from the 1997 murders. They also notice fresh flowers on Sam’s grave, indicating that someone recently paid their respects, which adds to the suspicion. An attack on Danica by the Fisherman prompts Teddy to insist they all move to Danica’s luxurious mansion for safety.
The tension escalates when Milo is strangled and taken away by the Fisherman, and the group becomes increasingly frantic. They discover that Judah knew Sam and that the police have been underreporting or ignoring key evidence. The murders continue with Teddy and Grant Spencer meeting their tragic ends. The survivors, now shocked by the loss of their friends, decide to flee Southport aboard Teddy’s yacht, hoping to find refuge elsewhere.
However, the horror isn’t over. Fallout from the murders reveals shocking truths: Judah was dead at his church with a photo of Sam and Stevie, exposing her as the real [Fisherman], seeking revenge for her past trauma. On the yacht, Stevie betrays everyone by attacking Ava and Danica, revealing herself as the mastermind behind the killings. She explains her motive, revealing her close connection to Sam and her desire for revenge, driven by past pain. She seeks to continue her vengeance by killing everyone on board, but Ray, Freddie Prinze Jr., who has been tending to Ava, intervenes. He shoots Stevie off the boat, saving the remaining survivors.
Back on land, as Ray recovers at his bar, Ava notices that Ray has an injury matching the wound she inflicted on the Fisherman, leading her to suspect that Ray is involved. The situation takes a darker turn when Julie discovers that Stevie, who appears to have survived, is still alive and taunting them with deadly intentions. Clued into the possibility of an ongoing threat, Julie reaches out to survivor Karla Wilson, seeking help to uncover who may be stalking them.
Throughout the ordeal, the characters confront the darkness hidden within their small town, unearthing long-buried secrets and facing the terrifying possibility that some wounds take more than a lifetime to heal—and that sometimes, evil refuses to stay dead.
