Senshiro Goda, the son of a household servant, nurtures a forbidden passion for Momoyo, his master's daughter, acutely aware of the chasm separating their social stations. He copes with this unrequited love by secretly witnessing Momoyo through a ceiling aperture, a ritual that brings him profound emotional torment. Possessing artistic talent, he channels his obsession into creating nude drawings of Momoyo without her knowledge. Discovery of these drawings by Momoyo's father results in Senshiro facing brutal punishment, reinforcing his lowly status. Following this, another housemaid, Tamao, tends to his injuries and reveals her own romantic feelings for him, yet Senshiro remains solely fixated on Momoyo.

His despair intensifies with the return of Momoyo's fiancé, Yoichiro, who intends to marry her and take her abroad. Senshiro observes disturbing events orchestrated by Yoichiro, including sadomasochistic activities and rituals involving multiple household members. These observations convince Senshiro the rituals form a dark ceremony aimed at summoning a demonic entity. Driven by protective instincts towards Momoyo and a desperate need to save her from what he perceives as a spreading curse of lust and sadism linked to Yoichiro, Senshiro resolves to act. He transforms from a passive witness into an active participant, dedicating himself to thwarting the demonic awakening and protecting Momoyo from the supernatural peril he believes threatens the household.