smile

At a psychiatric ward, therapist Dr. Rose Cotter meets with Laura Weaver, a graduate student. Weaver explains that she witnessed her art history professor commit suicide a few days earlier. Weaver then claims that an entity that only she can see, taking the form of smiling people, has been terrorizing her, and has told her that she is going to die, and nobody believed her when she told them. Soon after, Weaver stumbles to the floor and begins screaming. After Rose calls for help, she sees Laura standing up, calm and smiling. With a shard of broken pottery, Weaver kills herself by slitting her throat. Later, Rose sees a manic patient, Carl, smiling and shouting that she is going to die. Rose calls for nurses to restrain him, only to see he has been asleep the whole time. Concerned for Rose's mental well-being, her supervisor Dr. Morgan Desai gives her a week off.

In the following days, Rose's hallucinations continue. This leads those around her to believe she is unhinged and possibly dangerous. She visits her former therapist, Dr. Madeline Northcott, who suggests that her problems stem from her abusive and mentally ill mother, who died from an overdose, which she witnessed as a child.

Later, Rose attends her nephew's birthday party. The gift Rose had brought has been replaced by her dead cat, horrifying the children. This leads to a public breakdown in which she sees Stephanie, one of the party guests, smiling at her and trips back onto a glass table, hurting her wrist.

The incident convinces Rose that she has fallen victim to a curse. However, when Rose tries to tell her fiancé, Trevor, he doesn't understand. Both Trevor and the other guests become concerned for Rose's mental health.

Upon learning that Laura's professor was grinning at her before his death, Rose visits his widow, Victoria. Rose learns that the professor had also witnessed a suicide shortly before his own. Rose asks her ex-boyfriend Joel, a police detective, to go through old police records. They find several cases of people having commited suicide infront of someone else, all of whom had recently witnessed a suicide themselves.

Rose tries to patch things up with Holly and Trevor, but finds that Trevor is only out for himself and has called Madeline to help her get over the situation with Rose. Feeling betrayed, Rose chastises Trevor saying that she trusted him, and all he did was walk away from her when she needed him. Holly compares Rose's behavior to their late mother, but an enraged Rose, having had enough of being pushed around, responds by saying that Holly knows nothing of what happened.

Rose's hallucinations intensify. When Joel discovers that nearly all the witnesses died within a week of seeing the previous suicide, he comes to believe that Rose is cursed.

The only exception was Robert Talley, who instead murdered someone else. Rose and Joel visit him in jail, where he claims that the entity feeds on trauma, and the only way to escape it is to brutally kill someone in front of a witness to traumatize them. Rose angrily rejects the option and leaves. She is confronted at home by the entity in Madeline's form, where it gleefully warns her that she is running out of time. She impulsively drives to her hospital with a knife, and walks into the hospital and murders Carl in front of Morgan, but he rips his face off, revealing she is in another hallucination. Rose wakes up in her car. Morgan notices her with the knife, but she speeds away, prompting him to alert the police.

Rose drives to her abandoned family home, realizing that she cannot pass on the entity if she remains alone. Rose confronts the entity in the form of her mother, and it is revealed that as a child, Rose found her mother as she was dying from a drug overdose, but decided not to get help. The entity attacks Rose and pins her to the floor, but she smashes a lamp over its head, setting it on fire. She leaves the house, symbolically letting go of her trauma. Rose drives back to Joel's house, asking to stay the night, but Joel starts smiling at her and tells her he'll stay with her forever, showing that Rose was in a hallucination the whole time. Joel pulls up, having tracked Rose's phone. She panics and runs back inside, barricading herself in the house, so Joel cannot have the curse passed to him, but the entity reveals itself, having still been in the house, and rips off its skin to reveal its true form – a skinless, semi-humanoid monstrosity whose body is made from the previous victims that it consumed, with multiple sets of malformed jaws, nesting within an enormous, smiling mouth. The sight of the entity's true form is so frighteningly traumatic to Rose that it causes her to have a nervous breakdown and she falls into a trauma-induced paralysis. Having succeeded at finally breaking Rose's mind, the entity proceeds to feed on her culminated trauma by forcing itself inside her body through her mouth and merging with her psyche. Joel breaks down the front door and begins a short search, only to see Rose set herself on fire with a smile, passing the curse onto him.