Evy [Nina Kiri] Babic is a young woman raised in a Catholic household who now lives with her comatose mother, dedicating herself to her care. She and her friend Justin run The Undertone, a horror podcast that covers alleged supernatural events, with Evy tending to treat most claims as hoaxes while Justin remains convinced that something real is stirring beneath the surface. Their routine is upended when Justin receives an anonymous email that contains a cryptic string of letters and ten audio files, which they decide to play on the podcast.
The ten recordings come from a couple named Mike and Jessa, and Jessa speaks in her sleep. In the first recording, she sings "London Bridge" while asleep, and when Justin plays the file backward, he insists he can hear her whisper, "Mike, kill all." This unsettling moment drives Evy to explore hidden meanings in children’s songs, a line of inquiry that quickly becomes unsettling. When Evy tries playing her own favorite childhood lullaby, "Baa, Baa, Black Sheep," in reverse, she is shocked to hear the chilling message "lick the blood off." The more Evy investigates, the more she suspects something troubling is encoded in ordinary songs.
Soon after, Evy discovers she is six weeks pregnant. She confesses the news to her mother by her bedside, but she also admits she feels unfit to become a mother. She makes a tentative plan to visit a local women’s clinic, unsure of what awaits her. As she and Justin continue to sift through the Mike-and-Jessa recordings, more unsettling details emerge: Jessa’s voice in later clips seems to speak in gibberish that, when reversed, reveals the phrase "come in, Abyzou." Through their research, Evy and Justin learn that Abyzou is a demon from Mediterranean and European folklore, a figure said to cause miscarriages and to drive mothers to harm their own children out of jealousy because she herself was infertile.
Unnerving phenomena intensify around Evy. Her still-unconscious mother moves on her own, lights flicker without explanation, and a Virgin Mary statue Evy placed in the closet mysteriously appears in other parts of the house. The atmosphere grows increasingly claustrophobic as Evy grapples with her pregnancy, her supernatural discoveries, and the sense that something is watching from the shadows.
In a final, troubling twist within the audio files, Jessa insists she must “warn” someone who is listening, a line that hints at an impending danger. Justin tries to reply to the sender, but the email is automatically sent back to him. A caller, who claims to be Mike and Jessa’s neighbor, reveals that the couple was found dead in their home, their heads covered with plastic bags and walls canvassed in crayon drawings of babies; the autopsy shows Jessa was pregnant at the time of death. Another caller demands permission to speak to "Mary"—a name Evy had previously claimed she would someday use for her own child—and becomes relentless when Justin denies there is any such person. A final caller named Abby pleads for help calming a crying infant, but she ends up murdering the baby, leaving Evy and Justin pleading for mercy that is not granted.
As the tension peaks, Evy reveals that her mother has died, and she feels a crushing sense of guilt, believing she played a part in the loss by not praying for her. Rushing upstairs, Evy confronts a room transformed by fear: the walls are now covered in crayon drawings of Abyzou and of dead, bloodied infants. In a chilling moment, she sees her mother standing in the bathroom, and the scene erupts into a terrifying confrontation as she appears to be attacked while crying out for her to stop. The film closes on this unsettling convergence of myth, motherhood, and a family haunted by forces just out of reach, leaving Evy to confront the line between folklore and a very real, present danger.
