New Jersey, 1963. Alice Spages (Paula E. Sheppard
) is a 12-year old girl who lives with her mother, Catherine (Linda Miller
), and her younger sister, Karen (Brooke Shields
). Their father, Dominic (Niles McMaster
), is divorced from Catherine, and has recently re-married. Catherine and the girls live in a humble apartment, and their lives are very much centered on their Catholic parish. Both Alice and Karen go to the small Catholic school associated with their church, and all of the students wear church-issued yellow rain slickers as part of their uniforms. Karen is just about to make her first holy communion, but Alice seems to be jealous of the attention that Karen is getting because of it. Alice appears to have some major emotional problems. In the opening scene, Alice, Catherine and Karen are visiting the young priest Father Tom (Rudolph Willrich
) at the rectory, discussing Karen's upcoming first Holy Communion. Alice startles the rectory's housekeeper, Mrs. Tredoni (Mildred Clinton
), by wearing a bizarre transluscent mask, and she terrorizes Karen by stealing her doll and luring her to an abandoned building. While inside the building, Alice frightens Karen with the mask and briefly locks her in a room alone, threatening to never return her doll if she tells their mother about the incident. In the family's apartment, Alice takes Karen's communion veil and models it herself in a mirror; Karen causes a commotion over it and Catherine has to intervene.
Things go from bad to worse on the day of Karen's communion. As the parishoners sit in the pews waiting for the children to enter the sanctuary, Catherine and her younger sister Annie (Jane Lowry
) notice that Alice is not with them. Annie sends her daughter Angela (Kathy Rich
) to look for Alice. Before Karen can join the rest of the girls who are dressed in their white communion dresses and veils, she is attacked by a figure in one of the school's yellow rain slickers, wearing the same transluscent mask that Alice wears. The figure strangles Karen and then stows her body in a hollow bench, setting it on fire. Just before burning the body, the killer snatches the small cross that Karen wears around her neck, ripping the pendant from her body. Alice then appears among the younger girls, in Karen's place and wearing her veil, awaiting holy communion. Annie is outraged and urges Catherine to put a stop to it immediately. Shortly after, a nun notices the smoke and discovers Karen's body, her screams summoning the rest of the congregation. Annie sees Karen's body and melodramatically tells Catherine that her daughter is dead. Catherine breaks down crying. Alice slips Karen's veil into her pocket.
Dominic returns for Karen's funeral and Catherine weeps when she sees him. The domineering Annie imposes herself on Catherine and Alice, insisting that she will stay with them to help Catherine with anything she needs. Alice is resentful of Annie's presence, and wants to stay home with her mother instead of going back to school. Annie's obvious dislike for the girl gives way to accusations about Karen's murder; Annie points out the fact that Alice's whereabouts during the murder are unaccounted for. Catherine seems to be unwilling to admit that Alice acts strangely, insisting that nobody understands Alice like she does. She has to smooth over a confrontation between Annie and Alice, sending Alice on an errand to defuse the argument. She has Alice take the rent check to the family's landlord, Mr. Alphonso (Alphonso DeNoble
), who lives in one of the lower apartments of the building. Alphonso is a grotesque man, extremely obese and living in an apartment full of kittens; we see him feeding the kittens, referring to himself as "mommy", and then eating some of the moist cat food himself. Alphonso has repeatedly made jabs at Alice regarding Karen's death; he aligns himself with Alice's Aunt Annie, saying that Alice must have had something to do with Karen's murder. He also tells Alice that he knows about the odd shrine she has in the basement of the building, where she keeps various objects that she has either found or stolen, including the mask and Karen's missing doll. He tells Alice that Karen will return from the dead to collect her doll. When he makes inappropriate advances toward Alice and begins to touch her in a lewd manner, Alice throttles one of the kittens and strangles it to death and yelling "you never do that again!", upsetting Alphonso and allowing her to escape.
Meanwhile, the detectives investigating Karen's murder summon Alice's school records from the parish. When Dominic visits the police station to discuss Karen's case, he becomes hostile when Detective Brennan (Tom Signorelli
) suggests that he would like to question Alice about the murder. He phones the rectory to talk to Father Tom, with whom he is apparently familiar; at first his phone call is intercepted by Mrs. Tredoni, who is fiercely protective of the priests and the elderly monsignor who reside there. Tom picks up an extension and talks to Dominic, asking if they can meet in person. Dominic seems unaware of Alice's emotional problems, which have resulted in a number of questionable incidents at school. Father Tom tells him that Alice has a knack for causing trouble and making it seem like an accident.
Alice goes into the basement to her shrine, where she keeps her strange items, one of them being a jar full of large cockroaches, which she keeps alive by feeding them. She also still has Karen's doll. Alice puts on her mask. Upstairs, the mysterious figure wearing the yellow rain slicker and mask is creeping around the hallways. Annie goes to leave the apartment and she is attacked by the figure. The killer stands on the landing and slashes at Annie's legs and feet as she walks down the stairs, seriously wounding her. Before the killer can administer the death blow, Annie's screams summon Mr. Alphonso, who sees the killer's outfit and immediately identifies it as Alice. As the masked raincoat figure flees, Annie, who is hysterical and terrified, drags herself out into the street, where Catherine finds her. Dominic and Father Tom happen to pull up at the same time, in Father Tom's car. Tom and Catherine rush Annie to the hospital, while Dominic goes into the building to look for the person who attacked Annie. In the basement, he finds Alice at her shrine, terrified; she claims she saw Karen, apparently believing what Alphonso told her about Karen returning to claim her doll. Dominic comforts her; like Catherine, Dominic has never believed that Alice could be a killer.
At the hospital, Catherine tries to get Annie to recant her story about being attacked by "Alice", but Detective Cranston (Ted Tinling
) shows up to question Annie and she becomes hysterical, screaming that Alice was the one who stabbed her. They bring Alice into the police station to question her, giving her a lie detector test. Although Alice does not implicate herself, she gives a number of strange responses; one of the things that the lie detector machine reveals is that Alice sincerely believes that Karen is the one who attacked Aunt Annie. Alice resents being questioned, even lashing out at the policemen's lie detector machine, deliberately throwing it on the floor when they leave her alone with it. Although the police cannot charge her with either Karen's murder or Annie's slashing, they still feel she may be responsible for one or both, and they order her to have a psychological evaluation at the Sara Reed Children's Hospital. Catherine and Dominic are furious, but try to make the best of it. They visit Alice at the hospital together, discussing the case with the doctor who examines her, Dr. Whitman (Louisa Horton
). Dr. Whitman's evaluation seems especially damning, suggesting that Alice is schizophrenic and possibly dangerous. Whitman refuses to allow Alice to be released.
Dominic and Catherine have a quiet moment back at Catherine's apartment, when Catherine gets a strange phone call consisting of nothing but breathing; we see the caller is wearing the translucent mask. When the caller hangs up, Catherine assumes it was Annie; since Annie identified Alice as her attacker, Catherine vowed to disown Annie forever. Discussing the recent tragic events of their lives, Dominic and Catherine both agree that Alice could not have been responsible for all that's happened. Dominic suggests that perhaps Angela was the one who attacked Annie, which could explain why Alice thought she saw Karen, since they all wear the same yellow raincoat. Catherine, however, points out that Angela is an overweight young girl, and Karen was very petite, so it would be unlikely for Alice to confuse them. They wind up holding each other and beginning to make love, but are interrupted by a phone call from Dominic's wife, which breaks the mood.
Dominic returns to his hotel in time to receive a phone call from a sobbing voice; the caller identifies herself as Angela, saying that she ran away from home and needs Dominic to help her. She asks him to come to the abandoned building, the same one where Alice scared Karen at the beginning of the movie. When Dominic arrives, he sees the figure in the yellow raincoat and mask off in the distance. When he follows her into the building, she attacks him with the knife, stabbing him in the shoulder. Still unsure of who it is, Dominic follows her up a staircase, where the figure surprises him and bludgeons him repeatedly with a brick. With Dominic unconscious, the figure binds him with a cord and rolls him over to a loading door; the drop over the precipice is three or four stories to the ground. Dominic regains consciousness and realizes he is about to fall to his death. The killer removes the mask to reveal Mrs. Tredoni underneath. She rants about Dominic's relationship with Catherine, revealing that she knows that Alice was conceived before Dominic and Catherine were married. Dominic screams for help, but the area is too desolate for anybody to hear him. He uses his teeth to grab the crucifix that Mrs. Tredoni wears, the same one that she pulled from Karen's body the day she killed her. Mrs. Tredoni notices it and uses the brick to try and smash in Dominic's teeth. He refuses to give up the cross, swallowing it instead. Mrs. Tredoni, now furious, pushes him over the ledge and he falls to his death. Mrs. Tredoni then goes to the church, where a group of children are being instructed on how to make their first confession. Father Tom is the one who is going to hear the children, but he goes into the confessional to find that Mrs. Tredoni is already in there, changing out of the costume she wears to impersonate Alice. She pretends she is seeking to make a confession, and claims she feels guilty about having thoughts regarding the Monsignor; she says that he is in such poor health that she sometimes wishes he would pass away. Father Tom tells her she is a good woman, and that she doesn't need to come to confession about this since her thoughts are not sinful. He praises her for the care she has given himself and the other priests, and she is ecstatic when he calls her a friend.
The next day, Catherine becomes worried when she does not hear from Dominic, and she goes to the rectory to look for him; she reasons that since he has been borrowing Father Tom's car, he may be there. She is greeted by Mrs. Tredoni, who tries to get rid of her but finally allows her in to wait for Father Tom. Mrs. Tredoni is gutting fish for that evening's dinner, and she brings Catherine into the kitchen after preparing coffee for her. Catherine is uneasy, when Mrs. Tredoni reveals that she also had a daughter who died on the day of her first holy communion, Mrs. Tredoni seizes the knife and brandishes it toward Catherine while calling her a whore for having her own child out of wedlock. Father Tom returns and interrupts their conversation, telling Catherine that Dominic's body has been discovered. Catherine weeps in frustration and horror.
Dom's murder suggests that Alice is no longer a suspect, and Catherine is able to take her home. After they return, the figure in the yellow rain slicker and mask enters Alphonso's apartment while he is sleeping, and places the jar of roaches from Alice's secret shrine on his chest. Removing the mask, the figure reveals itself to be Alice herself. Catherine catches her leaving Alphonso's apartment, but Alice explains that she was only saying hello to him after returning from the hospital. Catherine praises her for being kind to him, and they leave to go to mass. Outside, Detective Cranston is watching the building as protection for Alice and Catherine. When they leave the building, Mrs. Tredoni slips in the back through the basement, wearing the yellow rain slicker and mask. She goes up to Catherine's apartment, apparently planning on murdering the first person she sees, but she finds the door locked. As she knocks on Catherine's door, Alphonso awakens and reacts in horror when the roaches begin to crawl over him. He starts screaming and alerts Cranston that something is wrong. Mrs. Tredoni hears it too, and she panics that he is drawing attention to the scene too soon. She runs back down the stairs, but Alphonso emerges and sees her running past his apartment. Thinking her to be Alice, he grabs her and starts to manhandle her, so she pulls out the butcher knife and stabs him in the chest several times. He stumbles back into his apartment and dies. When Mrs. Tredoni tries to escape through the basement, Cranston smashes down the front door and sees her. In her panic, she has forgotten to put the mask back on, and he easily identifies her.
Still wearing the yellow slicker, Mrs. Tredoni returns to the church and enters the sanctuary during service, making her way to where Alice and Catherine are sitting. Outside, the police arrive and discuss the best way to apprehend Mrs. Tredoni. Father Tom warns them not to try and confront her, as she is too close to Alice and her mother. Tom believes he can convince Mrs. Tredoni to come peacefully, since she adores him. During communion, Alice, Catherine, and Mrs. Tredoni all come up to the front side by side. Father Tom gives Catherine the wafer, but skips Alice. He also skips Mrs. Tredoni, instead leaning toward her and quietly asking her to go with the police. Mrs. Tredoni becomes indignant and asks why he will not give her communion; becoming furious, she shouts "But you give it to the whore!", pointing at Catherine. In a rage, Mrs. Tredoni pulls out the knife and stabs Father Tom through the throat. The congregation reacts in horror. Mrs. Tredoni clutches Father Tom to her as he dies, his blood pouring over the yellow rain slicker. Alice remains curiously detached from what is happening. In the confusion, a few policemen run into the church and arrest Mrs. Tredoni, while Alice has claimed Mrs. Tredoni's bag. Alice, still having not received communion, walks out of the church and pulls out the knife briefly, fondling the handle and smiling to herself.