Ghostface pays Sidney and her friends a third visit while they visit the set of "Stab 3", the third movie based upon the Woodsboro murders.
Cotton Weary, now living in Los Angeles and the host of a nationally syndicated television show, 100% Cotton, is called by Ghostface who demands the whereabouts of Sidney Prescott who has gone into seclusion since the events of Scream 2. He refuses and both Cotton and his girlfriend Christine are murdered.
Detective Mark Kincaid meets with Gale Weathers to discuss the murders prompting her to travel to Hollywood, where she finds Dewey Riley working as an advisor on the set of Stab 3, the third film in thefilm within a film series based on the Ghostface murders. Ghostface kills Stab 3 actress Sarah Darling with the help of a voice changer that can perfectly mimic various voices. Sidney is now living reclusively as a crisis counselor for an abused women's hotline, as she is terrified that another killer may strike. The killer begins taunting Sidney by phone, having discovered her phone number, forcing her out of hiding and drawing her to Hollywood. As the remaining Stab 3 cast gather at the home of Jennifer Jolie, Ghostface kills her bodyguard Steven Stone and uses a gas-leak to cause an explosion, killing fellow actorTom Prinze.
Dewey, Gale, Jennifer and the remaining "Stab 3" actors Angelina Tyler and Tyson Fox attend a birthday party for the director Roman Bridger where Ghostface strikes. Roman, Angelina, Tyson and Jennifer are apparently killed and Ghostface orders Sidney to the mansion to save Gale and Dewey's lives, as they are tied up. Sidney is forced to remove her firearm but reveals a hidden one, which she uses to shoot the killer. Detective Kincaid shows up but is knocked out. Sidney flees and hides in a secret screening room where she encounters Ghostface.
He reveals himself as Roman, having faked his death and survived being shot due to a bullet proof vest. Roman admits to being Sidney's half-brother, born to their mother Maureen Prescott when she was an actress in Hollywood. Roman details how, upon finding Maureen, she rejected him and he took his revenge by convincing Billy Loomis to kill her (sparking the events of Scream and Scream 2)and get an accomplice to frame, Stu Macher. However, when he discovered how much fame Sidney got because of those events, Roman snapped and lured Sidney out of hiding. Sidney and Roman fight, ending with Sidney fatally stabbing Roman. Dewey and Gale arrive and Roman attacks again, only for Dewey to kill him with a shot to the head.
In the aftermath of the murders, Dewey proposes to Gale, which she accepts as Sidney heads up the path to the house. Sidney is invited to join Dewey, Gale and Detective Kincaid to watch a scary movie. As she goes to join the others, a door behind her opens, but she walks away leaving it as is, finally confident that the murders have ended and that she is now safe.Source: Wikipedia