During the opening credits, Bergman can be overheard giving instructions to and discussing with his staff while preparing a shot.
The film is framed through the account of Alma (Ullmann), who addresses the audience directly. She tells of her husband's disappearance, which is explored in a flashback constructed of his diaries and her words.
Painter Johan Borg (von Sydow) and his young wife Alma live on the small island of Baltrum, where he seeks rest after a crisis which is not detailed. He is regularly approached by odd and suspicious people. He confides to Alma that he believes them to be demons, and begins to give names to them, including the Bird-Man, the Insects, the Meat-Eaters, the Schoolmaster (with pointers in his trousers) and The Lady With a Hat. Also, his insomnia grows worse. On the nights when Johan cannot sleep, Alma stays awake by his side.
One day, an old lady stops by the house and tells Alma to read Johan's diary, which he hides under his bed. Alma discovers that Johan is not only haunted by the real or imaginary strangers, but also by images of his former lover, Veronica Vogler (Ingrid Thulin).
The couple are approached by a Baron von Merkens (Erland Josephson), who lives in a nearby castle. The painter and his wife visit them and their surreal household. After dinner, the baron's wife (Gertrud Fridh) shows the couple into her bedroom, where on display is a portrait of Veronica by Borg. The painting appears to be so beautiful, the baron's wife proclaims, "It has become like a part of my solitary life. I love her." After Johan and Alma leave the castle, she confesses to him her fear of losing him to the demons, but also her will not to give up easily.
A superimposed title "Hour of the Wolf" marks the end of part one and the beginning of the second part. Again, Alma stays awake with Johan who cannot sleep. He tells her of the "vargtimmen" ("Hour of the Wolf"), during which, he says, most births and deaths occur. He also recounts his desperate love affair with Veronica and his childhood trauma of being locked into a cupboard where, as his parents said, a small man lived who fed on children's toes. Then he recalls a confrontation with a small boy which occurred some time ago and culminated in his killing of the boy. Whether this encounter actually took place or is imaginary is never revealed. Alma is shocked by Johan's confessions.
One of von Merken's guests shows up at the couple's house to invite them to another party at the castle, pointing out that Veronica Volger is among the invited guests. He places a pistol on the table, to protect them against "small animals", and leaves. Johan and Alma get into a fight over his obsession with Veronica. Johan finally picks up the pistol, shoots Alma and runs to the castle.
Johan attends the party. The baron's guests, all of whom previously attended, are revealed to be the demons that Johan described to Alma. As he rushes through the castle searching for Veronica, he meets the prophesied "Bird-Man", who applies cosmetics to his pale face and dresses him in a silk robe. He then leads Johan to her. Johan is humiliated as he finds the reunion a jest, with Veronica and the baron's guests laughing at his sincere, passionate display of love. Incredulous, he declares, "I thank you, the limit has finally been transgressed. The mirror has been shattered. But what do the splinters reflect?" Johan is physically attacked by the demons and flees into underbrush.
In the last act, Alma searches the forest for her husband. She witnesses the attacks on him, before he finally disappears, leaving her alone in the woods.
In the final scene, Alma addresses the camera, "Is it true that a woman who lives a long time with a man eventually winds up being like that man? I mean, she loves him, and tries to think like him, and see like him? They say it can change a person. I mean to say, if I had loved him much less, and not bothered so of everything about him, could I have protected him better?"
Hour of the Wolf originated from a manuscript with the working title "The Maneaters". Due to a severe case of pneumonia, Bergman had to interrupt his work on the project. After regaining his health, he wrote and directed Persona before returning to his earlier script which he re-wrote and filmed under the title Hour of the Wolf. Bergman confirmed that he felt the story being too personal and tried to create an artistic distance by including scenes of the shooting process and discussions with the actors. Except for the credits and the opening and final shot, Bergman removed these inserts prior to release. In The Passion of Anna, Bergman again made use of this technique.
Hour of the Wolf was released on 19 February 1968.
MGM released Hour of the Wolf both in the US and the UK in single-disc editions and as part of a box set including Shame, The Passion of Anna, The Serpent's Egg and Persona. The US release contains bonus material missing on the UK edition, while the UK box set omits the film Persona.
Hour of the Wolf has been well received by critics, and currently holds an approval rating of 88% on movie review aggregator website Rotten Tomatoes, based on seventeen reviews.
The New York Times opined that it is "not one of Bergman's great films but it is unthinkable for anyone seriously interested in movies not to see it." Time Out London called it "a brilliant gothic fantasy". Chicago Reader, on the other hand, called it "a magnificent failure".
In the British Film Institute's 2012 Sight & Sound polls, Hour of the Wolf received three critics' votes and 11 directors' votes, placing it at #44 in the latter poll. The aggregation site They Shoot Pictures, Don't They has found it to be the 345th most acclaimed film ever made.
Bergman later made the films Shame (1968) and The Passion of Anna (1969). Author Jerry Vermilye wrote that in exploring "the thread of violence intruding on ordinary lives," Hour of the Wolf, Shame and The Passion of Anna represent a trilogy. Author Amir Cohen-Shalev concurred the films form a trilogy.
WBAI's longest-running radio program takes its name from the film. The "Hour of the Wolf" radio show has run continuously since 1972 and concentrates on the literature of science fiction and fantasy.