Amber, Tulisa Contostavlos, is attacked and murdered in her home, and the police quickly label it a suicide attributed to investigator Bates, Ashley Walters. A group of troubled teens—Archie Robert Sheehan, Ricky Jacob Anderson, Ashleigh Shanika Warren-Markland, Cain, Samantha Emma Rigby, James Jack Doolan, Jasmine Jennie Jacques, and Kenny Jason Maza—have wrestled with suicidal thoughts for a long time, and Amber’s death pushes them to form a suicide pact, planning to carry it out at Ashleigh’s party.
As Samantha writes a suicide diary in the college dressing rooms, she is stabbed by a masked killer. Meanwhile, Kenny, with his friend Davey, rigs up cameras around Ashleigh’s house so the footage can be released later, turning tragedy into notoriety. Archie and Jasmine begin a romance, and Archie suggests they remove themselves from the pact, but Jasmine resists and questions whether anyone can truly escape the plan they set in motion.
The following day the group is shaken by Samantha’s death. At college, Jasmine is attacked but manages to phone the police and locks herself in a room. Archie finds her and is questioned by Bates and Mason, who seem to think Jasmine is suffering from a condition that made her imagine the attack. At night, Ashleigh, Ricky, Cain, and James gather to discuss who could have attacked Jasmine, while they hesitate about whether to continue with the suicide pact. Elsewhere, Kenny, now being filmed for a suicide diary, decides he will shoot everyone at Ashleigh’s party so his death will be more famous. The next day, while walking down the road, James encounters a bully, Curtis, but the rest of the group defends him. The group then meets with Kenny and tells him they are not going to go through with the plan, angering him. Mr. Hudson, a teacher at the college, makes a cryptic phone call to an unknown receiver, claiming he is out of the deal. Returning home, Hudson discovers his wife dead and himself murdered.
As the group tries to figure out who the killer is, suspicion falls on nearly everyone. At night, while making his way to Ashleigh’s party, Ricky—believing he hears Samantha’s voice—has his throat slit by the killer. While party guests remain inside, Bates and Mason patrol the grounds. Curtis and his date go to the bathroom, where both are stabbed to death. Outside, Kenny and Davey arrive, but Bates and Mason stop Kenny before he can enter the house with his gun. As partygoers begin to leave, James is stabbed to death in the kitchen; Ashleigh witnesses this and is chased into the garden. The killer cuts the electricity, sending the rest of the partygoers home, and when Ashleigh tries to get their attention, she is stabbed and dragged away.
Archie and Jasmine, who have been spending time alone together, return to the party to find the house empty. Inside, they are stalked in the dark and discover Cain and Davey’s bodies, and are eventually split up. Moments later, Jasmine emerges from the house distraught, while Bates enters the house and finds Archie dead. Outside, Jasmine reaches the police car and finds both Mason and Kenny murdered, before Bates attacks her, revealing himself to be the killer. As he is about to kill Jasmine, Archie reveals himself to have faked his own murder and attacks Bates, giving Jasmine an opportunity to shoot him. As Jasmine tends to an injured Archie, Bates narrates the line, “Demons never die,” before opening his eyes.
