Bộ phim lấy bối cảnh tại thành phố Đài Bắc sau một năm chống chọi với đại dịch virus Alvin (một biến thể giả tưởng của virus cúm). Mọi chuyện trở nên tồi tệ khi virus đột ngột đột biến, không biến nạn nhân thành những thây ma vô hồn mà biến họ thành những kẻ sát nhân điên cuồng, tàn bạo và cực kỳ biến thái.

"Finally," the man croaked, his voice raspy. "I can show you how much I've hated this silence."

One of the primary themes explored in "The Sadness" is the psychological impact of trauma on individuals and relationships. The movie delves into the complexities of the human psyche, showcasing how traumatic experiences can shape our perceptions, emotions, and interactions with others. The film also touches on the idea of disconnection and isolation, highlighting the couple's struggles to cope with their past and find solace in each other.

A good Vietsub translates his quote: "We are all two seconds away from being monsters. The virus just removes the two-second delay."

Infected individuals (dubbed "Sadists") are not mindless zombies. They are fully conscious but completely stripped of empathy and morality. They want to inflict the most painful, humiliating, and sadistic acts imaginable.

The Vietnamese subtitles (Vietsub) add an extra layer of accessibility for Vietnamese-speaking audiences, allowing them to fully immerse themselves in the movie's intense atmosphere.