Ellen Carpenter Lee Grant is a successful but emotionally repressed astronomer living in Los Angeles, sharing a dilapidated house in the Hollywood Hills with her sister, Cissy Carol Kane. Their home, inherited from their late father Max, a globe-trotting anthropologist who studied in Africa, is stacked with memories and artifacts that blur the line between science, art, and something darker. Cissy [Carol Kane] is portrayed as mentally imbalanced and childlike, never fully able to manage life on her own. She spends most of her days tending to a menagerie of pet monkeys—what she calls “mafus”—which occupy a large cage in the living room. Yet these animals rarely survive under her care, battered by sudden outbursts of violence that leave the house echoing with their unfortunate ends.
The tension between the two sisters escalates when Cissy grows furious after Ellen refuses to adopt another mafu. The sisterly bond frays further as Cissy fixates on Ellen in a troubling, almost incestuous way. She even threatens suicide if Ellen won’t fulfill her demand for a king colobus monkey, a request Ellen eventually concedes to, hoping to placate her volatile sister. Their godfather, Zom Will Geer, a zoologist, becomes a reluctant provider of exotic animals. When he cannot secure a colobus, he arrives with an orangutan instead, an animal that instantly captivates Cissy and seems to validate her fragile sense of purpose.
Meanwhile, Ellen begins a romance with David Eastman James Olson, a coworker at the Griffith Observatory. Ellen is cautious about letting anyone into the intimate chaos of her family life, and her hesitancy grows as she senses how the sisters’ dynamics may affect both of them. The moment Cissy learns of David, her fragile composure shatters; she redoubles her efforts for attention, and the pressure culminates in a brutal act: she uses a chain to kill the orangutan that had enthralled her and destroys any sense of normalcy in the house.
Ellen heads out for a work trip to Arizona, leaving Cissy alone for several days in the house. When David returns, intending to find Ellen, he is met by Cissy, who escorts him inside and parades the house’s African artifacts—the relics their father gathered—before revealing her own disturbing theories about them. She explains how their father built the mafu cage inside the home so he could study his subjects without being physically separated from his daughters. The atmosphere tightens as the two share drinks and dance to tribal music, eventually drifting into the mafu cage itself. In a chilling moment, Cissy chains David to shackles on the wall, a gesture he initially mistakes as a joke, but she commits to locking him inside.
From there, Cissy treats David as an anthropological subject, observing him with clinical detachment as night falls. In a ritualistic turn, she paints her face red, dons tribal regalia, and re-enacts rituals she learned about from their father’s work. Armed with an ornate wooden club, she carries out a violent act and murders David, burying his body in the garden. When Ellen returns and stumbles upon a portrait that resembles David, a cold dread settles over her. She finds blood-soaked clothing in the laundry, confirming her worst fears, and retreats to the bathroom, where a tense struggle unfolds as Cissy experiences a full-blown nervous breakdown.
Hours pass, and Ellen, newly emerged from the bathroom, finds herself trapped by Cissy, who shackles her inside the mafu cage. Ellen resists eating and challenges the likelihood of help coming, warning that Cissy will be institutionalized once authorities learn the truth about Ellen’s fate. The struggle leaves Ellen increasingly weak, while Cissy experiences a fervent, unstable surge of ritualistic energy, sketching an ornate mural on the cage walls as the environment grows more claustrophobic and ominous. Ellen’s life ebbs away, and the house settles into a somber stillness as her sister’s fixation hardens into a grim, self-imposed sentence.
In the end, Ellen dies, the sisters’ tragic dynamic sealed in a single, devastating moment. After laying Ellen to rest in burial garb, Cissy slips into the mafu cage herself and binds her own fate to the same fate she imposed on others, shackling herself to the wall as the house holds its breath. The once-bright rooms of the home become a tomb of memories—an eerie tableau of love warped by fear, control, and a lineage of obsession that neither science nor sanity can fully explain.
