On Valentine's Day in 1900, students from Appleyard College, a prestigious girls' school located in Victoria, Australia, prepare for a memorable picnic at Hanging Rock to celebrate St. Valentine. The group is led by teachers Miss Greta McCraw and Mlle. de Poitiers. However, one student, Sara, a quiet orphan who has been separated from her older brother Bertie, must remain at the college under the supervision of Miss Lumley and the stern headmistress Mrs. Appleyard.
As the day unfolds, the adventurous students—Miranda, Marion, Irma, and Edith—decide to wander away from the picnic. They happen upon a young Englishman, Michael Fitzhubert, and his Australian friend, Albert Crundell. Climbing the Rock, the girls succumb to a mysterious force and drift into sleep. When Edith awakens in sheer horror, her panicked scream sends her rushing back, while Miranda, Marion, and Irma venture deeper into a hidden crevice of the ancient rock formation.
Upon realizing that Miss McCraw and the three girls have vanished, the remaining students are engulfed in concern. A police investigation begins, but no signs emerge, despite Edith's fragmented recollections which include sighting Miss McCraw in a state of distress and perceiving a peculiar red cloud.
Hounded by nightmares of the mysterious disappearances, Michael takes it upon himself to organize a search for the missing girls alongside Albert. He decides to stay overnight at the Rock and awakens to find Irma alive within the crevice, although he succumbs to heat exhaustion shortly after. When Albert brings the police back to the site, Michael discreetly hands him a piece of Irma's dress as a clue. However, when Albert finds Irma, she is unable to recall anything about her time away or the fates of Miranda, Marion, or Miss McCraw.
The shock of these disappearances sends ripples of chaos through the college, causing many students to depart and stirring unrest within the community. Media attention grows as Michael endures haunting dreams, symbolized by the elusive presence of a white swan representing Miranda. Meanwhile, Mrs. Appleyard informs Sara that her guardian has neglected to contact the school, leaving her tuition unpaid. This revelation threatens Sara's future at Appleyard, leading to her exclusion from extracurricular activities, and she begins to languish in bed, pining for her lost friend Miranda.
Irma, now back from the ordeal but with lost memories, is set to leave for Europe to reunite with her family. During a farewell visit to the college amid a dance lesson, she is besieged by her classmates, who vehemently question her innocence and memory loss. After her tearful departure, Mlle. de Poitiers discovers that Miss Lumley has been restricting Sara's movement under the pretense of correct posture during the lesson.
As Easter approaches, tensions heighten when Mrs. Appleyard visits Sara, informing her that she must leave the college and return to the orphanage unless her fees are settled. Although Mrs. Appleyard's demeanor is cold, she eventually breaks down in private, overwhelmed by the implications of their conversation. The following day, Albert experiences a dream about Sara, who bids him farewell among her cherished flowers. In a moment of concern, Mrs. Appleyard meets with Mlle. de Poitiers, who previously expressed worry for Sara's well-being. She deceitfully assures her that Sara's guardian has come to collect her.
Later, tragedy strikes when Sara's body is found in the greenhouse; it appears she jumped from the roof, shattering through the glass. The gardener rushes to inform Mrs. Appleyard of the incident, only to discover her eerily calm, dressed for a funeral, with her luggage already prepared. A haunting voiceover reveals that Mrs. Appleyard, grappling with the collapse of her college and haunted by the unsettling events, was discovered deceased at the foot of Hanging Rock—an apparent victim of the very mystery that has enveloped the community.
In a poignant flashback to the picnic day, it is reiterated that the disappearances of Miranda, Marion, and Miss McCraw endure as unresolved enigmas, casting a long shadow over the local populace.
