What Is Killer Nun About?
The premise of Killer Nun in 302 words, with nothing given away. The full story follows below.
In a dimly lit Catholic infirmary tucked away from the bustling streets, a whispered dossier of Vatican secrets looms over the everyday rituals of care. The hospital, a sanctuary for the elderly, is governed as much by liturgy as by medical charts, creating a world where sacred rites clash with the stark realities of aging bodies. The corridors echo with hushed prayers, the scent of incense mingles with antiseptic, and an unsettling stillness suggests that not everything is as orderly as the immaculate façade implies.
Sister Gertrude returns to this cloistered environment after a harrowing operation, burdened by lingering doubts about her health and a growing dependence on potent narcotics. As the head nurse, she straddles the line between religious devotion and clinical responsibility, her once‑steady composure increasingly frayed by an inner turbulence that she can neither name nor fully conceal. Around her, Mother Superior attempts to uphold the convent’s strict code, while Sister Mathieu offers a quiet, ambiguous companionship that hints at deeper, unspoken currents beneath the surface.
The film’s tone is a slow‑burning blend of gothic horror and psychological drama, bathing every scene in a muted, cold light that accentuates the institutional claustrophobia. Characters move through sterile rooms and echoing chapels with a palpable sense of restraint, their interactions tinged with an uneasy mixture of reverence, desire, and hidden fear. The atmosphere suggests that the hospital itself is a character—a labyrinthine space where the boundaries between duty, obsession, and faith become dangerously blurred.
Within this unsettling setting, Sister Gertrude’s struggle resonates as a meditation on control and surrender, inviting viewers to question how much of what we see is shaped by belief, by addiction, or by the shadows that linger in spaces meant for healing. The narrative promises a tense, immersive experience that lingers long after the final prayer fades.
What Happens in Killer Nun?
The complete story of Killer Nun, from the first scene to the last, in 597 words (about 3 minutes). Spoilers throughout. Names in the text link to 3 cast member pages.
Spoilers ahead
Sister Gertrude, Anita Ekberg, a nun who works in a Catholic hospital for the elderly, returns to work after brain tumor surgery, carrying a heavy cloud of anxiety. She is convinced that her cancer has returned, even as the hospital’s lead doctor, Dr. Poirret [Massimo Serato], assures her there is no medical evidence of recurrence. The convent’s Mother Superior, Alida Valli, dismisses her fears as hypochondria, while Sister Mathieu, who has an unspoken attraction to Gertrude, believes Gertrude’s worry is legitimate.
Unbeknownst to the others, Gertrude begins living a double life. She slips into the city to seek sexual encounters with random men and, in a troubling turn, begins to intravenously abuse morphine and heroin that Sister Mathieu steals for her from the hospital. Dr. Poirret notes a troubling change in her personality as she starts mistreating patients and immerses herself in reading graphic hagiographies about the lives of tortured saints. The strain of her behavior eventually leads to Poirret being fired from the hospital.
In a drug-fueled episode, Sister Mathieu’s grandfather, a patient at the hospital, is bludgeoned to death with a lamp and his body is defenestrated to look like a suicide. Sister Mathieu discovers Gertrude’s veil with the body and, swearing loyalty, vows not to implicate her, promising to burn the evidence to hide what happened.
After Poirret’s dismissal, the hospital hires a new physician, Dr. Patrick Roland, Joe Dallesandro. In a stormy night scene, Gertrude witnesses Jonathan, an elderly patient, having sex with a young female orderly outside. She later awakens from a nightmare in which she suffocates Jonathan, but she cannot tell if it was merely a dream or a murder she has committed. The next morning, Jonathan’s body is found in the grass, and Gertrude leads a prayer for him before suffering a nervous breakdown. Shortly after, Janet, another patient, is bound and gagged by an unseen assailant and later stabbed in the face with needles and slashed in the head and neck with a scalpel.
After Janet’s body is discovered hanging in an elevator shaft, Dr. Roland sedates a panicked Gertrude. When she awakens, she confronts Peter, a middle-aged patient on crutches, who claims to know who is committing the killings but will not reveal further details. Gertrude believes him and even steals his crutches, but Peter’s body is later found in the boiler room. Gertrude is escorted out of the hospital and confronted by the Mother Superior, who scolds her and has her sent to an isolation cell to be sedated.
Meanwhile, Sister Mathieu confesses to Dr. Roland about stealing drugs to help Gertrude and threatens suicide if she is exposed. She then begins to seduce him, intensifying the hospital’s tense, morally ambiguous atmosphere. Isolated in her cell, Gertrude detoxes from the drugs and, as clarity returns, recalls the first murder—the grandfather killed by Sister Mathieu. Gertrude realizes, with mounting horror, that she had been intoxicated and misattributing the killings to herself, while Sister Mathieu was the true killer, driven by the sexual abuse she suffered as a child at the hands of her grandfather.
As the truth surfaces, the film reveals a devastating dynamic: the apparent string of murders at the hospital is rooted in a cycle of trauma, manipulation, and self-deception. Gertrude’s drug-soaked perception leads her to believe she is the killer, only to uncover that Sister Mathieu was acting from a history of abuse and a desperate response to her pain. The resolution leaves the audience with a haunting meditation on guilt, memory, and the blurred line between victim and predator within a claustrophobic, institutional setting.
Killer Nun Timeline: Every Key Event in Order
13 key events in the order they happen, from “Gertrude returns to work after brain surgery” to “Gertrude's memory reveals the truth”. 13 events name a place, across 6 locations.
- 1
Gertrude returns to work after brain surgery
Sister Gertrude returns to the Catholic hospital for the elderly after surgery to remove a brain tumor. She is plagued by anxiety, convinced that her cancer has returned, despite reassurances from Dr. Poirret. The Mother Superior dismisses her symptoms as hypochondria, while Sister Mathieu privately contends that the worry is legitimate.
When:Immediately after surgery Where:Catholic hospital for the elderly
- 2
Gertrude begins a double life and drugs
She starts venturing into the city to pursue sexual encounters and begins intravenously abusing morphine and heroin that Sister Mathieu steals from the hospital. Dr. Poirret notes a troubling change in her personality as she mistreats patients. She also revels in reading gory hagiographies about tortured saints, signaling a disturbing new fixation.
When:Shortly after returning to work Where:City and hospital
- 3
Gertrude causes Poirret's dismissal
Exploiting her transformation, Gertrude engineers the dismissal of Dr. Poirret from the hospital. The scandal and her increasingly erratic behavior create an atmosphere of fear and shifting loyalties. A replacement is eventually hired to fill Poirret's position.
When:After Poirret's dismissal Where:Hospital
- 4
Grandfather killed; veil found
While Gertrude is in a drug-induced state, Sister Mathieu's grandfather, a hospital patient, is bludgeoned to death with a lamp and defenestrated to look like suicide. Sister Mathieu discovers Gertrude's veil on the body and pledges to protect her, promising to burn the evidence to hide it.
When:During Gertrude's drug-induced period Where:Hospital
- 5
New doctor arrives
Dr. Patrick Rowland is hired as Poirret's replacement, signaling a shift in hospital leadership. Gertrude's manipulation continues to shape the institutional response as new staff settle in. The atmosphere grows tenser as more deaths occur.
When:After Poirret's dismissal Where:Hospital
- 6
Rainstorm revelation and nightmare
During a rainstorm, Gertrude witnesses Jonathan, an elderly patient, having sex with a young orderly outside the hospital. She later awakes from a nightmare in which she suffocates Jonathan, unsure if the dream is real. The next morning, Jonathan's corpse is found lying in the grass.
When:During a rainstorm; next morning Where:Outside the hospital grounds
- 7
Gertrude's nervous breakdown
The events surrounding Jonathan push Gertrude into a nervous breakdown as she struggles to distinguish reality from dangerous fantasies. Her grip on sanity continues to slip as more violence unfolds within the hospital. She becomes increasingly isolated from others.
When:Right after Jonathan's death Where:Hospital
- 8
Janet is attacked and murdered
Janet, another patient, is bound and gagged by an unseen assailant and ritually stabbed in the face with needles, her head and neck slashed by a scalpel. The brutal crime shocks the hospital community and deepens the sense that a killer is at work. Gertrude remains uncertain about her own role in the violence.
When:Shortly after Jonathan's death Where:Hospital
- 9
Janet's body found; Gertrude sedated
Janet's lifeless body is found hanging in an elevator shaft, prompting panic and a controlled response from the staff. Dr. Poirret sedates a panicked Gertrude to prevent further breakdown. The investigation into the murders intensifies as the hospital tries to maintain order.
When:After Janet's body is discovered Where:Hospital
- 10
Confrontation with Peter and his death
Gertrude confronts Peter, a middle-aged patient on crutches, who claims to know who is committing the killings. She believes she is being framed, but Peter refuses to reveal more. Later, Peter's body is found in the boiler room and Gertrude steals his crutches in a moment of frantic desperation.
When:After the confrontation Where:Hospital
Show the other 3 events of Killer Nun Hide the last 3 events
- 11
Mother Superior isolates Gertrude
The Mother Superior scolds Gertrude for her behavior and has her escorted to an isolation cell where she will be sedated. The hospital's mechanism of control tightens as Gertrude is cut off from others. Her withdrawal deepens as she remains separated from the world outside.
When:Immediately after Peter's death Where:Hospital
- 12
Sister Mathieu confesses; Dr. Roland entangled
Sister Mathieu confesses to Dr. Roland that she has been stealing drugs to aid Gertrude and threatens suicide if she is exposed. She then begins to seduce him, complicating the hospital's already tangled web of loyalties. The confession ties her to the unfolding violence.
When:During isolation period Where:Hospital/Dr Roland's office
- 13
Gertrude's memory reveals the truth
While detoxing in her isolation cell, Gertrude recalls the hospital's first murder—the grandfather of Sister Mathieu—and realizes Mathieu was the perpetrator. She understands that her own violent perceptions were fueled by drug haze, not actual guilt. The revelation leaves her psychologically fragile, still dependent on drugs and haunted by the truth.
When:During detox; later realization Where:Isolation cell
Who Are the Main Characters in Killer Nun?
7 characters, among them Sister Gertrude — Anita Ekberg, Mother Superior — Alida Valli and Dr. Poirret — Massimo Serato: who each one is and the part they play in the story. Every profile links to the actor’s page.
- SG
Sister Gertrude — Anita Ekberg
Played by Anita Ekberg
A nun at a Catholic hospital who spirals from a brain-tumor recovery into drug-aided brutality and a double life. Her anxiety, mood swings, and moments of intoxication fuel a disturbing pattern of coercion and violence. The hospital setting magnifies her inner conflict between faith and desire.
- 💊 Drug-abuse
- ⛪ Nun
- 😨 Troubled
-
Mother Superior — Alida Valli
Played by Alida Valli
Authority within the convent-hospital who dismisses Gertrude's fears as hypochondria. She represents institutional control, policing behavior, and the pressure to maintain appearances. Her decisions about Gertrude's confinement reflect the moral rigidity of the setting.
- ⛪ Authority
- 😶 Judgmental
- 🛡️ Controlling
- DP
Dr. Poirret — Massimo Serato
Played by Massimo Serato
The hospital's lead doctor who initially reassures Gertrude there is no cancer relapse and later becomes a casualty of the power shift in the hospital. His firing symbolizes the shift from traditional medical authority to a new order.
- 💊 Medical-authority
- 🩺 Doctor
- 😟 Skeptical
- DP
Dr. Patrick Rowland — Joe Dallesandro
Played by Joe Dallesandro
The handsome replacement doctor whose presence introduces a new dynamic in patient care and power structures within the hospital. He becomes a key observer of Gertrude's behavior and the escalating crisis.
- 🩺 Doctor
- 👨⚕️ New presence
- 🧭 Turning point
-
Peter — Lou Castel
Played by Lou Castel
A middle-aged patient on crutches who claims to know who is behind the killings. His cryptic presence and subsequent death contribute to the mystery and paranoia surrounding Gertrude.
- 🧭 Mysterious
- 🦴 Crutch-user
- 🕵️ Clue
- J—
Janet — Sofia Lusy
Played by Sofia Lusy
A patient who is bound, gagged, and brutally stabbed, her death heightening the sense of danger in the hospital. Her murder is a focal point in the unraveling crisis and the investigation into the killer.
- 🎭 Victim
- 🔪 Murdered
- 😱 Suspense
- SM
Sister Mathieu — Paola Morra
Played by Paola Morra
A Sister with unspoken sexual attraction to Gertrude, who steals drugs for her and ultimately confesses to the doctor. Her backstory of abuse and her manipulation challenge the narrative of who is truly responsible.
- 💊 Drug-theft
- 💔 Trauma survivor
- 🎭 Manipulative
Where and When Is Killer Nun Set?
Killer Nun is set in Catholic hospital for the elderly. Here is why the place matters to the story.
Where
Catholic hospital for the elderly
Set inside a Catholic hospital for the elderly run by a convent, the building and its wards frame the story's tension between care, authority, and hidden sins. The long corridors, patient rooms, and a chapel-like atmosphere create a claustrophobic stage for Gertrude's double life. The setting emphasizes the clash between religious duty and human fragility, anchoring the psychological horror.
- 🏥 Hospital for the elderly
- ⛪ Convent-affiliated
- 🌆 Urban setting
What Are the Themes of Killer Nun?
5 ideas the story keeps returning to, among them Faith, Duality and Addiction.
-
01
Faith
A nun's vocation defines Gertrude's outward role while her inner life spirals into addiction and violence. The hospital’s religious authority magnifies questions of sin, guilt, and redemption. Faith here is both a source of solace and a mask that conceals psychological rot. The film uses religious imagery to heighten moral tension around her actions.
-
02
Duality
Gertrude leads a double life, moving between cloistered duty and city lurid encounters. The narrative plays with perception, leaving viewers unsure whether the murders stem from Gertrude's hand or from her drug haze. The revelation reframes everything, challenging initial judgments about guilt. The hospital setting intensifies the sense of a fractured identity under pressure.
-
03
Addiction
Morphine and heroin misuse blur boundaries between healing and harm. The drug dependency drives Gertrude into increasingly unstable behavior and detaches her from reality. Dependency escalates the sense of danger, affecting her judgment and the fate of patients. The plot uses addiction to explore how vulnerability can erode moral boundaries.
-
04
Murder
A string of violent acts punctuates the hospital drama, with Janet's brutal stabbing heightening the sense of danger in the wards. The murders are shown through shifting perspectives, inviting doubt about who is truly responsible. The twists reframe the events as driven by hidden motivations beyond a single culprit. The finale challenges what viewers accepted as truth.
-
05
Trauma
Sister Mathieu's history of childhood abuse emerges as a driving force behind the violence, reframing the killer's motive. The film treats trauma as a powerful factor shaping loyalty, sexuality, and survival. The relationship between Mathieu and Gertrude exposes survivor guilt and moral ambiguity. The resolution redirects blame toward a deeper wound rather than a straightforward villain.
What Kind of Film Is Killer Nun?
Dark in tone, with steady pacing and a moderate story, going by the plot summary.
- Tone
- Dark
- Pacing
- Steady
- Story
- Moderate
- Intensity
- High
- Ending
- Bleak
An intensely sleazy and paranoid horror film set in a claustrophobic Catholic hospital where a morphine-addicted nun's descent into madness blurs the line between victim and predator amidst a series of brutal murders.
- claustrophobic
- anxious
- oppressive
- sleazy
- paranoid
- nightmarish
- addiction
- religious hypocrisy
- repressed trauma
- cycle of abuse
Content notes: sexual violence, torture, drug abuse, murder, psychological trauma, sexual perversion.
Quiz
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Where to Watch Killer Nun
Stream it on ARROW and FlixFling, or rent or buy it from Apple TV Store and FlixFling. US availability and prices from JustWatch.
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