The pre-credit opening is of the sound of a projector and an image of an old projector coal lamp, followed by a rapid succession of seemingly random images: a shorn lamb, a crawling spider, an animated drawing of a girl rowing upside-down, a nail driven into a hand, spikes on a railing, a snowy park-like setting. Then, interior shots of a morgue with distant sounds of hospital utensils and dripping water. A boy and an older woman, both apparently dead, lie on beds covered with sheets. A phone shatters the silence; the boy wakes and tries vainly to go back to sleep. He gets up and wipes the translucent glass on a door; a woman's face emerges slowly. The credits roll, interspersed with rapid shots from the pre-credit sequence and recurring flashes of the boy's face.

The film shifts to a hospital, where a doctor is briefing a young nurse, Alma, about a patient, Elisabet Vogler, an actress who has withdrawn from her family and profession and become mute. Having expressed doubts about her suitability to be her nurse, Alma introduces herself to the patient, who does not respond. She turns on the radio which is playing Bach, Elisabet covers her face as the camera gradually darkens, obliterating her features. At home, Alma gives herself a pep talk about how good her life is; she is engaged and she likes her job. Alma reads a letter to Elisabet from her husband. Elisabet tears to pieces the enclosed picture of her son. Later when she is alone she turns on the TV. A news report shows a monk in Vietnam burning himself to death. Horrified, she retreats to a corner of the room.

The doctor, discussing her condition with her, tells Elisabet her silence is just another role which she will soon discard. He advises the two women to spend time at his summerhouse on an island. The voice of Bergman describes their harmonious existence there. While Elisabet remains mute, Alma becomes increasingly talkative. After an evening of drinking she tells of an orgy in which she took part. Later on the same day she made love to her fiancé, became pregnant and had an abortion. At this point in her story Alma breaks down crying and is embraced by Elisabet.

Sitting at the kitchen table, Alma tells Elisabet they are alike and, in a drunken stupor, hears Elisabet urging her to go to bed. That night, Elisabet goes to Alma's bed but when questioned about it the next day denies it.

Driving to post some mail the following day, Alma reads a letter from Elisabet to her doctor which she had forgotten to seal, which recounts how she is recovering and, in a patronising tone, how devoted Alma is to her. The scene ends with a shot of Alma in a slick raincoat, her figure reflected in a pond.

Back at the house Alma, offended by Elisabet's letter, deliberately neglects to pick up some broken glass on the patio. Observed by Alma, Elisabet steps on it and cuts herself. At this moment of crisis the film breaks and when it starts again it is in slow motion and out of focus. When it is adjusted we see the two women dressed in black reading on the beach. Alma is restless, Elisabet at peace. Begging Elisabet to speak to her, Alma becomes hysterical, but is well aware of her own hysteria. In the kitchen, she threatens Elisabet with a pot of boiling water and is triumphant when she elicits a frightened response.

Elisabet is next seen walking quickly on the beach, pursued by the stumbling Alma who begs her forgiveness. Elisabet ignores her and the scene ends with Alma alone crouching among the rocks. That night Mr. Vogler visits but Alma takes Elisabet's place in bed with him.

The second part of the film comprises scenes with an obscure narrative. Alma and Elisabet are seen sitting at a table. Alma slits her arm and Elisabet sucks her blood. In the next scene Alma enters dressed in a nurse's uniform. On the table in front of Elisabet is the torn picture of her son. Sitting opposite Alma starts to talk of Elisabet's feelings for the child. Then the camera projects the same scene from Elisabet's viewpoint, focussing on Alma's face. Alma's composure breaks down as she denies her likeness to Elisabet. The scene ends with the two faces merging into one.

In the next scene we are back in the hospital room. Alma asks Elisabet to speak the word "nothing". Elisabet's silence is broken. We then return to the summerhouse where Alma is carrying in garden furniture and locking up. Later she departs alone by bus.

The film flickers. A brief shot shows Elisabet in a film studio. The equipment gradually shuts down. The film has ended.